diff --git a/mocha-config/puppeteer-unit-tests.js b/mocha-config/puppeteer-unit-tests.js
index 23fb4f8cfa329..fb11fd18d0d4c 100644
--- a/mocha-config/puppeteer-unit-tests.js
+++ b/mocha-config/puppeteer-unit-tests.js
@@ -18,8 +18,9 @@ const base = require('./base');
 
 module.exports = {
   ...base,
-  require: ['./test/mocha-utils.js'],
-  spec: 'test/*.spec.js',
+  require: ['ts-node/register', './test/mocha-utils.ts'],
+  spec: 'test/*.spec.ts',
+  extension: ['ts'],
   parallel: process.env.CI && !process.env.COVERAGE,
   // retry twice more, so we run each test up to 3 times if needed.
   retries: process.env.CI ? 2 : 0,
diff --git a/package.json b/package.json
index 80a1f4a861c45..cf516d67b0723 100644
--- a/package.json
+++ b/package.json
@@ -63,7 +63,8 @@
     "@microsoft/api-extractor": "7.8.12",
     "@types/debug": "0.0.31",
     "@types/mime": "^2.0.0",
-    "@types/node": "^10.17.14",
+    "@types/mocha": "^7.0.2",
+    "@types/node": "^14.0.13",
     "@types/proxy-from-env": "^1.0.1",
     "@types/rimraf": "^2.0.2",
     "@types/tar-fs": "^1.16.2",
@@ -89,6 +90,7 @@
     "prettier": "^2.0.5",
     "sinon": "^9.0.2",
     "text-diff": "^1.0.1",
+    "ts-node": "^8.10.2",
     "typescript": "3.9.2"
   },
   "browser": {
diff --git a/src/common/Browser.ts b/src/common/Browser.ts
index 8aa7d7a291ad6..474b8c93f1213 100644
--- a/src/common/Browser.ts
+++ b/src/common/Browser.ts
@@ -310,7 +310,7 @@ export class BrowserContext extends EventEmitter {
 
   waitForTarget(
     predicate: (x: Target) => boolean,
-    options: { timeout?: number }
+    options: { timeout?: number } = {}
   ): Promise<Target> {
     return this._browser.waitForTarget(
       (target) => target.browserContext() === this && predicate(target),
diff --git a/src/common/Coverage.ts b/src/common/Coverage.ts
index 4b2d5a046d7db..d9537dd0ddbff 100644
--- a/src/common/Coverage.ts
+++ b/src/common/Coverage.ts
@@ -36,10 +36,12 @@ export class Coverage {
     this._cssCoverage = new CSSCoverage(client);
   }
 
-  async startJSCoverage(options: {
-    resetOnNavigation?: boolean;
-    reportAnonymousScripts?: boolean;
-  }): Promise<void> {
+  async startJSCoverage(
+    options: {
+      resetOnNavigation?: boolean;
+      reportAnonymousScripts?: boolean;
+    } = {}
+  ): Promise<void> {
     return await this._jsCoverage.start(options);
   }
 
@@ -47,9 +49,11 @@ export class Coverage {
     return await this._jsCoverage.stop();
   }
 
-  async startCSSCoverage(options: {
-    resetOnNavigation?: boolean;
-  }): Promise<void> {
+  async startCSSCoverage(
+    options: {
+      resetOnNavigation?: boolean;
+    } = {}
+  ): Promise<void> {
     return await this._cssCoverage.start(options);
   }
 
diff --git a/src/common/FrameManager.ts b/src/common/FrameManager.ts
index 243c6c3da4d0d..6e56c75332952 100644
--- a/src/common/FrameManager.ts
+++ b/src/common/FrameManager.ts
@@ -417,10 +417,12 @@ export class Frame {
     return await this._frameManager.navigateFrame(this, url, options);
   }
 
-  async waitForNavigation(options: {
-    timeout?: number;
-    waitUntil?: PuppeteerLifeCycleEvent | PuppeteerLifeCycleEvent[];
-  }): Promise<HTTPResponse | null> {
+  async waitForNavigation(
+    options: {
+      timeout?: number;
+      waitUntil?: PuppeteerLifeCycleEvent | PuppeteerLifeCycleEvent[];
+    } = {}
+  ): Promise<HTTPResponse | null> {
     return await this._frameManager.waitForFrameNavigation(this, options);
   }
 
@@ -523,7 +525,11 @@ export class Frame {
 
   async click(
     selector: string,
-    options: { delay?: number; button?: MouseButtonInput; clickCount?: number }
+    options: {
+      delay?: number;
+      button?: MouseButtonInput;
+      clickCount?: number;
+    } = {}
   ): Promise<void> {
     return this._secondaryWorld.click(selector, options);
   }
@@ -584,7 +590,7 @@ export class Frame {
 
   async waitForSelector(
     selector: string,
-    options: WaitForSelectorOptions
+    options: WaitForSelectorOptions = {}
   ): Promise<ElementHandle | null> {
     const handle = await this._secondaryWorld.waitForSelector(
       selector,
@@ -599,7 +605,7 @@ export class Frame {
 
   async waitForXPath(
     xpath: string,
-    options: WaitForSelectorOptions
+    options: WaitForSelectorOptions = {}
   ): Promise<ElementHandle | null> {
     const handle = await this._secondaryWorld.waitForXPath(xpath, options);
     if (!handle) return null;
diff --git a/src/common/Input.ts b/src/common/Input.ts
index 7a49b224b122a..e423808922722 100644
--- a/src/common/Input.ts
+++ b/src/common/Input.ts
@@ -122,7 +122,7 @@ export class Keyboard {
     return !!keyDefinitions[char];
   }
 
-  async type(text: string, options: { delay?: number }): Promise<void> {
+  async type(text: string, options: { delay?: number } = {}): Promise<void> {
     const delay = (options && options.delay) || null;
     for (const char of text) {
       if (this.charIsKey(char)) {
diff --git a/src/common/JSHandle.ts b/src/common/JSHandle.ts
index cd88bb662a6ad..4273db864cd90 100644
--- a/src/common/JSHandle.ts
+++ b/src/common/JSHandle.ts
@@ -430,7 +430,7 @@ export class ElementHandle extends JSHandle {
    * uses {@link Page.mouse} to click in the center of the element.
    * If the element is detached from DOM, the method throws an error.
    */
-  async click(options: ClickOptions): Promise<void> {
+  async click(options: ClickOptions = {}): Promise<void> {
     await this._scrollIntoViewIfNeeded();
     const { x, y } = await this._clickablePoint();
     await this._page.mouse.click(x, y, options);
diff --git a/src/common/Page.ts b/src/common/Page.ts
index a8d184ea549c2..2ded9343f9f21 100644
--- a/src/common/Page.ts
+++ b/src/common/Page.ts
@@ -44,7 +44,7 @@ import Protocol from '../protocol';
 
 const writeFileAsync = helper.promisify(fs.writeFile);
 
-interface Metrics {
+export interface Metrics {
   Timestamp?: number;
   Documents?: number;
   Frames?: number;
@@ -129,14 +129,13 @@ const paperFormats: Record<string, PaperFormat> = {
   a6: { width: 4.13, height: 5.83 },
 } as const;
 
-enum VisionDeficiency {
-  none = 'none',
-  achromatopsia = 'achromatopsia',
-  blurredVision = 'blurredVision',
-  deuteranopia = 'deuteranopia',
-  protanopia = 'protanopia',
-  tritanopia = 'tritanopia',
-}
+type VisionDeficiency =
+  | 'none'
+  | 'achromatopsia'
+  | 'blurredVision'
+  | 'deuteranopia'
+  | 'protanopia'
+  | 'tritanopia';
 
 /**
  * All the events that a page instance may emit.
@@ -837,7 +836,7 @@ export class Page extends EventEmitter {
     return await this._frameManager.mainFrame().content();
   }
 
-  async setContent(html: string, options: WaitForOptions): Promise<void> {
+  async setContent(html: string, options: WaitForOptions = {}): Promise<void> {
     await this._frameManager.mainFrame().setContent(html, options);
   }
 
@@ -913,11 +912,11 @@ export class Page extends EventEmitter {
     );
   }
 
-  async goBack(options: WaitForOptions): Promise<HTTPResponse | null> {
+  async goBack(options: WaitForOptions = {}): Promise<HTTPResponse | null> {
     return this._go(-1, options);
   }
 
-  async goForward(options: WaitForOptions): Promise<HTTPResponse | null> {
+  async goForward(options: WaitForOptions = {}): Promise<HTTPResponse | null> {
     return this._go(+1, options);
   }
 
@@ -1005,7 +1004,14 @@ export class Page extends EventEmitter {
   }
 
   async emulateVisionDeficiency(type?: VisionDeficiency): Promise<void> {
-    const visionDeficiencies = new Set(Object.keys(VisionDeficiency));
+    const visionDeficiencies = new Set([
+      'none',
+      'achromatopsia',
+      'blurredVision',
+      'deuteranopia',
+      'protanopia',
+      'tritanopia',
+    ]);
     try {
       assert(
         !type || visionDeficiencies.has(type),
@@ -1356,7 +1362,7 @@ export class Page extends EventEmitter {
   }
 
   waitForFunction(
-    pageFunction: Function,
+    pageFunction: Function | string,
     options: {
       timeout?: number;
       polling?: string | number;
diff --git a/src/common/Puppeteer.ts b/src/common/Puppeteer.ts
index 0a8a0a8c6ad87..e81ca0af9a145 100644
--- a/src/common/Puppeteer.ts
+++ b/src/common/Puppeteer.ts
@@ -134,7 +134,7 @@ export class Puppeteer {
     return puppeteerErrors;
   }
 
-  defaultArgs(options: ChromeArgOptions): string[] {
+  defaultArgs(options: ChromeArgOptions = {}): string[] {
     return this._launcher.defaultArgs(options);
   }
 
diff --git a/src/index.ts b/src/index.ts
index 3df618f8c3874..6adf9e0b36bf9 100644
--- a/src/index.ts
+++ b/src/index.ts
@@ -31,4 +31,4 @@ const puppeteer = initializePuppeteer({
  * And therefore consuming via require('puppeteer') would break / require the user
  * to access require('puppeteer').default;
  */
-module.exports = puppeteer;
+export = puppeteer;
diff --git a/src/node/BrowserFetcher.ts b/src/node/BrowserFetcher.ts
index b4082a771f8fc..4f879da6b0eef 100644
--- a/src/node/BrowserFetcher.ts
+++ b/src/node/BrowserFetcher.ts
@@ -215,7 +215,7 @@ export class BrowserFetcher {
    */
   async download(
     revision: string,
-    progressCallback: (x: number, y: number) => void
+    progressCallback: (x: number, y: number) => void = (): void => {}
   ): Promise<BrowserFetcherRevisionInfo> {
     const url = downloadURL(
       this._product,
diff --git a/test/CDPSession.spec.js b/test/CDPSession.spec.ts
similarity index 90%
rename from test/CDPSession.spec.js
rename to test/CDPSession.spec.ts
index 43d0aad381e42..299364809dcd4 100644
--- a/test/CDPSession.spec.js
+++ b/test/CDPSession.spec.ts
@@ -14,13 +14,14 @@
  * limitations under the License.
  */
 
-const { waitEvent } = require('./utils');
-const expect = require('expect');
-const {
+import { waitEvent } from './utils';
+import expect from 'expect';
+import {
   getTestState,
   setupTestBrowserHooks,
   setupTestPageAndContextHooks,
-} = require('./mocha-utils');
+  describeChromeOnly,
+} from './mocha-utils';
 
 describeChromeOnly('Target.createCDPSession', function () {
   setupTestBrowserHooks();
@@ -35,7 +36,7 @@ describeChromeOnly('Target.createCDPSession', function () {
       client.send('Runtime.enable'),
       client.send('Runtime.evaluate', { expression: 'window.foo = "bar"' }),
     ]);
-    const foo = await page.evaluate(() => window.foo);
+    const foo = await page.evaluate(() => globalThis.foo);
     expect(foo).toBe('bar');
   });
   it('should send events', async () => {
@@ -96,6 +97,9 @@ describeChromeOnly('Target.createCDPSession', function () {
     expect(error.message).toContain('ThisCommand.DoesNotExist');
 
     async function theSourceOfTheProblems() {
+      // This fails in TS as it knows that command does not exist but we want to
+      // have this tests for our users who consume in JS not TS.
+      // @ts-expect-error
       await client.send('ThisCommand.DoesNotExist');
     }
   });
diff --git a/test/EventEmitter.spec.js b/test/EventEmitter.spec.ts
similarity index 84%
rename from test/EventEmitter.spec.js
rename to test/EventEmitter.spec.ts
index b6fcc91952433..9e1d227284f5c 100644
--- a/test/EventEmitter.spec.js
+++ b/test/EventEmitter.spec.ts
@@ -1,6 +1,22 @@
-const { EventEmitter } = require('../lib/common/EventEmitter');
-const sinon = require('sinon');
-const expect = require('expect');
+/**
+ * Copyright 2020 Google Inc. All rights reserved.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+import { EventEmitter } from '../src/common/EventEmitter';
+import sinon from 'sinon';
+import expect from 'expect';
 
 describe('EventEmitter', () => {
   let emitter;
@@ -10,7 +26,7 @@ describe('EventEmitter', () => {
   });
 
   describe('on', () => {
-    const onTests = (methodName) => {
+    const onTests = (methodName: 'on' | 'addListener'): void => {
       it(`${methodName}: adds an event listener that is fired when the event is emitted`, () => {
         const listener = sinon.spy();
         emitter[methodName]('foo', listener);
@@ -39,7 +55,7 @@ describe('EventEmitter', () => {
   });
 
   describe('off', () => {
-    const offTests = (methodName) => {
+    const offTests = (methodName: 'off' | 'removeListener'): void => {
       it(`${methodName}: removes the listener so it is no longer called`, () => {
         const listener = sinon.spy();
         emitter.on('foo', listener);
diff --git a/test/accessibility.spec.js b/test/accessibility.spec.ts
similarity index 99%
rename from test/accessibility.spec.js
rename to test/accessibility.spec.ts
index 5f223ecfe6393..618be6009126b 100644
--- a/test/accessibility.spec.js
+++ b/test/accessibility.spec.ts
@@ -14,12 +14,13 @@
  * limitations under the License.
  */
 
-const expect = require('expect');
-const {
+import expect from 'expect';
+import {
   getTestState,
   setupTestBrowserHooks,
   setupTestPageAndContextHooks,
-} = require('./mocha-utils');
+  describeFailsFirefox,
+} from './mocha-utils';
 
 describeFailsFirefox('Accessibility', function () {
   setupTestBrowserHooks();
diff --git a/test/assets/input/textarea.html b/test/assets/input/textarea.html
index 6d5be760740f0..6d77f3106d31e 100644
--- a/test/assets/input/textarea.html
+++ b/test/assets/input/textarea.html
@@ -7,9 +7,9 @@
     <textarea></textarea>
     <script src='mouse-helper.js'></script>
     <script>
-      window.result = '';
-      let textarea = document.querySelector('textarea');
+      globalThis.result = '';
+      globalThis.textarea = document.querySelector('textarea');
       textarea.addEventListener('input', () => result = textarea.value, false);
     </script>
   </body>
-</html>
\ No newline at end of file
+</html>
diff --git a/test/assets/shadow.html b/test/assets/shadow.html
index 7242e673b562a..3796ca768c44d 100644
--- a/test/assets/shadow.html
+++ b/test/assets/shadow.html
@@ -1,8 +1,8 @@
 <script>
 
 let h1 = null;
-let button = null;
-let clicked = false;
+window.button = null;
+window.clicked = false;
 
 window.addEventListener('DOMContentLoaded', () => {
   const shadowRoot = document.body.attachShadow({mode: 'open'});
diff --git a/test/browser.spec.js b/test/browser.spec.ts
similarity index 96%
rename from test/browser.spec.js
rename to test/browser.spec.ts
index f20db1f657319..af2c71f8fcf8d 100644
--- a/test/browser.spec.js
+++ b/test/browser.spec.ts
@@ -14,8 +14,8 @@
  * limitations under the License.
  */
 
-const expect = require('expect');
-const { getTestState, setupTestBrowserHooks } = require('./mocha-utils');
+import expect from 'expect';
+import { getTestState, setupTestBrowserHooks } from './mocha-utils';
 
 describe('Browser specs', function () {
   setupTestBrowserHooks();
diff --git a/test/browsercontext.spec.js b/test/browsercontext.spec.ts
similarity index 97%
rename from test/browsercontext.spec.js
rename to test/browsercontext.spec.ts
index 8d29a6ab9db27..b8f4cfcf0be44 100644
--- a/test/browsercontext.spec.js
+++ b/test/browsercontext.spec.ts
@@ -14,9 +14,13 @@
  * limitations under the License.
  */
 
-const expect = require('expect');
-const { getTestState, setupTestBrowserHooks } = require('./mocha-utils');
-const utils = require('./utils');
+import expect from 'expect';
+import {
+  getTestState,
+  setupTestBrowserHooks,
+  itFailsFirefox,
+} from './mocha-utils';
+import utils from './utils';
 
 describe('BrowserContext', function () {
   setupTestBrowserHooks();
diff --git a/test/chromiumonly.spec.js b/test/chromiumonly.spec.ts
similarity index 98%
rename from test/chromiumonly.spec.js
rename to test/chromiumonly.spec.ts
index 1a46c4b719e34..8c0ee81e9eb4f 100644
--- a/test/chromiumonly.spec.js
+++ b/test/chromiumonly.spec.ts
@@ -13,12 +13,13 @@
  * See the License for the specific language governing permissions and
  * limitations under the License.
  */
-const expect = require('expect');
-const {
+import expect from 'expect';
+import {
   getTestState,
   setupTestBrowserHooks,
   setupTestPageAndContextHooks,
-} = require('./mocha-utils');
+  describeChromeOnly,
+} from './mocha-utils';
 
 describeChromeOnly('Chromium-Specific Launcher tests', function () {
   describe('Puppeteer.launch |browserURL| option', function () {
diff --git a/test/click.spec.js b/test/click.spec.ts
similarity index 86%
rename from test/click.spec.js
rename to test/click.spec.ts
index cc8be5a6806a6..3e85ceeaed154 100644
--- a/test/click.spec.js
+++ b/test/click.spec.ts
@@ -14,13 +14,14 @@
  * limitations under the License.
  */
 
-const expect = require('expect');
-const {
+import expect from 'expect';
+import {
   getTestState,
   setupTestPageAndContextHooks,
   setupTestBrowserHooks,
-} = require('./mocha-utils');
-const utils = require('./utils');
+  itFailsFirefox,
+} from './mocha-utils';
+import utils from './utils';
 
 describe('Page.click', function () {
   setupTestBrowserHooks();
@@ -30,7 +31,7 @@ describe('Page.click', function () {
 
     await page.goto(server.PREFIX + '/input/button.html');
     await page.click('button');
-    expect(await page.evaluate(() => result)).toBe('Clicked');
+    expect(await page.evaluate(() => globalThis.result)).toBe('Clicked');
   });
   it('should click svg', async () => {
     const { page } = getTestState();
@@ -41,7 +42,7 @@ describe('Page.click', function () {
         </svg>
       `);
     await page.click('circle');
-    expect(await page.evaluate(() => window.__CLICKED)).toBe(42);
+    expect(await page.evaluate(() => globalThis.__CLICKED)).toBe(42);
   });
   itFailsFirefox(
     'should click the button if window.Node is removed',
@@ -51,7 +52,7 @@ describe('Page.click', function () {
       await page.goto(server.PREFIX + '/input/button.html');
       await page.evaluate(() => delete window.Node);
       await page.click('button');
-      expect(await page.evaluate(() => result)).toBe('Clicked');
+      expect(await page.evaluate(() => globalThis.result)).toBe('Clicked');
     }
   );
   // @see https://github.com/puppeteer/puppeteer/issues/4281
@@ -67,7 +68,7 @@ describe('Page.click', function () {
         <span onclick='javascript:window.CLICKED=42'></span>
       `);
     await page.click('span');
-    expect(await page.evaluate(() => window.CLICKED)).toBe(42);
+    expect(await page.evaluate(() => globalThis.CLICKED)).toBe(42);
   });
   it('should not throw UnhandledPromiseRejection when page closes', async () => {
     const { page } = getTestState();
@@ -76,7 +77,7 @@ describe('Page.click', function () {
     await Promise.all([
       newPage.close(),
       newPage.mouse.click(1, 2),
-    ]).catch((error) => {});
+    ]).catch(() => {});
   });
   it('should click the button after navigation ', async () => {
     const { page, server } = getTestState();
@@ -85,7 +86,7 @@ describe('Page.click', function () {
     await page.click('button');
     await page.goto(server.PREFIX + '/input/button.html');
     await page.click('button');
-    expect(await page.evaluate(() => result)).toBe('Clicked');
+    expect(await page.evaluate(() => globalThis.result)).toBe('Clicked');
   });
   itFailsFirefox('should click with disabled javascript', async () => {
     const { page, server } = getTestState();
@@ -108,7 +109,7 @@ describe('Page.click', function () {
         <span onclick='javascript:window.CLICKED = 42;'><i>woof</i><b>doggo</b></span>
       `);
     await page.click('span');
-    expect(await page.evaluate(() => window.CLICKED)).toBe(42);
+    expect(await page.evaluate(() => globalThis.CLICKED)).toBe(42);
   });
   it('should select the text by triple clicking', async () => {
     const { page, server } = getTestState();
@@ -162,17 +163,17 @@ describe('Page.click', function () {
 
     await page.goto(server.PREFIX + '/wrappedlink.html');
     await page.click('a');
-    expect(await page.evaluate(() => window.__clicked)).toBe(true);
+    expect(await page.evaluate(() => globalThis.__clicked)).toBe(true);
   });
 
   it('should click on checkbox input and toggle', async () => {
     const { page, server } = getTestState();
 
     await page.goto(server.PREFIX + '/input/checkbox.html');
-    expect(await page.evaluate(() => result.check)).toBe(null);
+    expect(await page.evaluate(() => globalThis.result.check)).toBe(null);
     await page.click('input#agree');
-    expect(await page.evaluate(() => result.check)).toBe(true);
-    expect(await page.evaluate(() => result.events)).toEqual([
+    expect(await page.evaluate(() => globalThis.result.check)).toBe(true);
+    expect(await page.evaluate(() => globalThis.result.events)).toEqual([
       'mouseover',
       'mouseenter',
       'mousemove',
@@ -183,23 +184,23 @@ describe('Page.click', function () {
       'change',
     ]);
     await page.click('input#agree');
-    expect(await page.evaluate(() => result.check)).toBe(false);
+    expect(await page.evaluate(() => globalThis.result.check)).toBe(false);
   });
 
   itFailsFirefox('should click on checkbox label and toggle', async () => {
     const { page, server } = getTestState();
 
     await page.goto(server.PREFIX + '/input/checkbox.html');
-    expect(await page.evaluate(() => result.check)).toBe(null);
+    expect(await page.evaluate(() => globalThis.result.check)).toBe(null);
     await page.click('label[for="agree"]');
-    expect(await page.evaluate(() => result.check)).toBe(true);
-    expect(await page.evaluate(() => result.events)).toEqual([
+    expect(await page.evaluate(() => globalThis.result.check)).toBe(true);
+    expect(await page.evaluate(() => globalThis.result.events)).toEqual([
       'click',
       'input',
       'change',
     ]);
     await page.click('label[for="agree"]');
-    expect(await page.evaluate(() => result.check)).toBe(false);
+    expect(await page.evaluate(() => globalThis.result.check)).toBe(false);
   });
 
   it('should fail to click a missing button', async () => {
@@ -243,10 +244,10 @@ describe('Page.click', function () {
 
     await page.goto(server.PREFIX + '/input/button.html');
     await page.evaluate(() => {
-      window.double = false;
+      globalThis.double = false;
       const button = document.querySelector('button');
-      button.addEventListener('dblclick', (event) => {
-        window.double = true;
+      button.addEventListener('dblclick', () => {
+        globalThis.double = true;
       });
     });
     const button = await page.$('button');
@@ -265,14 +266,14 @@ describe('Page.click', function () {
       button.style.left = '368px';
     });
     await page.click('button');
-    expect(await page.evaluate(() => window.result)).toBe('Clicked');
+    expect(await page.evaluate(() => globalThis.result)).toBe('Clicked');
   });
   it('should click a rotated button', async () => {
     const { page, server } = getTestState();
 
     await page.goto(server.PREFIX + '/input/rotatedButton.html');
     await page.click('button');
-    expect(await page.evaluate(() => result)).toBe('Clicked');
+    expect(await page.evaluate(() => globalThis.result)).toBe('Clicked');
   });
   it('should fire contextmenu event on right click', async () => {
     const { page, server } = getTestState();
@@ -304,7 +305,7 @@ describe('Page.click', function () {
     const frame = page.frames()[1];
     const button = await frame.$('button');
     await button.click();
-    expect(await frame.evaluate(() => window.result)).toBe('Clicked');
+    expect(await frame.evaluate(() => globalThis.result)).toBe('Clicked');
   });
   // @see https://github.com/puppeteer/puppeteer/issues/4110
   xit('should click the button with fixed position inside an iframe', async () => {
@@ -325,7 +326,7 @@ describe('Page.click', function () {
       button.style.setProperty('position', 'fixed')
     );
     await frame.click('button');
-    expect(await frame.evaluate(() => window.result)).toBe('Clicked');
+    expect(await frame.evaluate(() => globalThis.result)).toBe('Clicked');
   });
   itFailsFirefox(
     'should click the button with deviceScaleFactor set',
@@ -345,7 +346,7 @@ describe('Page.click', function () {
       const frame = page.frames()[1];
       const button = await frame.$('button');
       await button.click();
-      expect(await frame.evaluate(() => window.result)).toBe('Clicked');
+      expect(await frame.evaluate(() => globalThis.result)).toBe('Clicked');
     }
   );
 });
diff --git a/test/cookies.spec.js b/test/cookies.spec.ts
similarity index 99%
rename from test/cookies.spec.js
rename to test/cookies.spec.ts
index 2408518889ad3..63092f2aa3991 100644
--- a/test/cookies.spec.js
+++ b/test/cookies.spec.ts
@@ -13,12 +13,13 @@
  * See the License for the specific language governing permissions and
  * limitations under the License.
  */
-const expect = require('expect');
-const {
+import expect from 'expect';
+import {
   getTestState,
   setupTestBrowserHooks,
   setupTestPageAndContextHooks,
-} = require('./mocha-utils');
+  itFailsFirefox,
+} from './mocha-utils';
 
 describe('Cookie specs', () => {
   setupTestBrowserHooks();
diff --git a/test/coverage-utils.js b/test/coverage-utils.js
index aea76803fc326..3cc51bd1e4ee4 100644
--- a/test/coverage-utils.js
+++ b/test/coverage-utils.js
@@ -14,6 +14,9 @@
  * limitations under the License.
  */
 
+// TODO (@jackfranklin): convert this to TypeScript and enable type-checking
+// @ts-nocheck
+
 /* We want to ensure that all of Puppeteer's public API is tested via our unit
  * tests but we can't use a tool like Istanbul because the way it instruments
  * code unfortunately breaks in Puppeteer where some of that code is then being
diff --git a/test/coverage.spec.js b/test/coverage.spec.ts
similarity index 97%
rename from test/coverage.spec.js
rename to test/coverage.spec.ts
index df5fe21a60a09..9f38434d1c7cc 100644
--- a/test/coverage.spec.js
+++ b/test/coverage.spec.ts
@@ -14,12 +14,13 @@
  * limitations under the License.
  */
 
-const expect = require('expect');
-const {
+import expect from 'expect';
+import {
   getTestState,
   setupTestPageAndContextHooks,
   setupTestBrowserHooks,
-} = require('./mocha-utils');
+  describeChromeOnly,
+} from './mocha-utils';
 
 describe('Coverage specs', function () {
   describeChromeOnly('JSCoverage', function () {
@@ -122,6 +123,8 @@ describe('Coverage specs', function () {
       const coverage = await page.coverage.stopJSCoverage();
       expect(
         JSON.stringify(coverage, null, 2).replace(/:\d{4}\//g, ':<PORT>/')
+        // TODO (@jackfranklin) extend the Expect typedefs to fix this
+        // @ts-expect-error toBeGolden matcher
       ).toBeGolden('jscoverage-involved.txt');
     });
     describe('resetOnNavigation', function () {
@@ -224,6 +227,8 @@ describe('Coverage specs', function () {
       const coverage = await page.coverage.stopCSSCoverage();
       expect(
         JSON.stringify(coverage, null, 2).replace(/:\d{4}\//g, ':<PORT>/')
+        // TODO (@jackfranklin) extend the Expect typedefs to fix this
+        // @ts-expect-error toBeGolden matcher
       ).toBeGolden('csscoverage-involved.txt');
     });
     it('should ignore injected stylesheets', async () => {
diff --git a/test/defaultbrowsercontext.spec.js b/test/defaultbrowsercontext.spec.ts
similarity index 97%
rename from test/defaultbrowsercontext.spec.js
rename to test/defaultbrowsercontext.spec.ts
index 67862e1f714e2..e4cba19015545 100644
--- a/test/defaultbrowsercontext.spec.js
+++ b/test/defaultbrowsercontext.spec.ts
@@ -13,12 +13,13 @@
  * See the License for the specific language governing permissions and
  * limitations under the License.
  */
-const expect = require('expect');
-const {
+import expect from 'expect';
+import {
   getTestState,
   setupTestBrowserHooks,
   setupTestPageAndContextHooks,
-} = require('./mocha-utils');
+  itFailsFirefox,
+} from './mocha-utils';
 
 describe('DefaultBrowserContext', function () {
   setupTestBrowserHooks();
diff --git a/test/dialog.spec.js b/test/dialog.spec.ts
similarity index 95%
rename from test/dialog.spec.js
rename to test/dialog.spec.ts
index 126ebec14589d..3b762ff5ac3d7 100644
--- a/test/dialog.spec.js
+++ b/test/dialog.spec.ts
@@ -13,14 +13,15 @@
  * See the License for the specific language governing permissions and
  * limitations under the License.
  */
-const expect = require('expect');
-const sinon = require('sinon');
+import expect from 'expect';
+import sinon from 'sinon';
 
-const {
+import {
   getTestState,
   setupTestPageAndContextHooks,
   setupTestBrowserHooks,
-} = require('./mocha-utils');
+  itFailsFirefox,
+} from './mocha-utils';
 
 describe('Page.Events.Dialog', function () {
   setupTestBrowserHooks();
diff --git a/test/elementhandle.spec.js b/test/elementhandle.spec.ts
similarity index 87%
rename from test/elementhandle.spec.js
rename to test/elementhandle.spec.ts
index 2e66f8378b5cb..38af4b6648c87 100644
--- a/test/elementhandle.spec.js
+++ b/test/elementhandle.spec.ts
@@ -14,14 +14,17 @@
  * limitations under the License.
  */
 
-const expect = require('expect');
-const {
+import expect from 'expect';
+import {
   getTestState,
   setupTestBrowserHooks,
   setupTestPageAndContextHooks,
-} = require('./mocha-utils');
+  describeFailsFirefox,
+  itFailsFirefox,
+} from './mocha-utils';
 
-const utils = require('./utils');
+import utils from './utils';
+import { ElementHandle } from '../src/common/JSHandle';
 
 describe('ElementHandle specs', function () {
   setupTestBrowserHooks();
@@ -98,12 +101,10 @@ describe('ElementHandle specs', function () {
       // Step 1: Add Frame and position it absolutely.
       await utils.attachFrame(page, 'frame1', server.PREFIX + '/resetcss.html');
       await page.evaluate(() => {
-        const frame = document.querySelector('#frame1');
-        frame.style = `
-          position: absolute;
-          left: 1px;
-          top: 2px;
-        `;
+        const frame = document.querySelector<HTMLElement>('#frame1');
+        frame.style.position = 'absolute';
+        frame.style.left = '1px';
+        frame.style.top = '2px';
       });
 
       // Step 2: Add div and position it absolutely inside frame.
@@ -112,17 +113,15 @@ describe('ElementHandle specs', function () {
         await frame.evaluateHandle(() => {
           const div = document.createElement('div');
           document.body.appendChild(div);
-          div.style = `
-          box-sizing: border-box;
-          position: absolute;
-          border-left: 1px solid black;
-          padding-left: 2px;
-          margin-left: 3px;
-          left: 4px;
-          top: 5px;
-          width: 6px;
-          height: 7px;
-        `;
+          div.style.boxSizing = 'border-box';
+          div.style.position = 'absolute';
+          div.style.borderLeft = '1px solid black';
+          div.style.paddingLeft = '2px';
+          div.style.marginLeft = '3px';
+          div.style.left = '4px';
+          div.style.top = '5px';
+          div.style.width = '6px';
+          div.style.height = '7px';
           return div;
         })
       ).asElement();
@@ -177,15 +176,29 @@ describe('ElementHandle specs', function () {
       await page.goto(server.PREFIX + '/input/button.html');
       const button = await page.$('button');
       await button.click();
-      expect(await page.evaluate(() => result)).toBe('Clicked');
+      expect(await page.evaluate(() => globalThis.result)).toBe('Clicked');
     });
     it('should work for Shadow DOM v1', async () => {
       const { page, server } = getTestState();
 
       await page.goto(server.PREFIX + '/shadow.html');
-      const buttonHandle = await page.evaluateHandle(() => button);
-      await buttonHandle.click();
-      expect(await page.evaluate(() => clicked)).toBe(true);
+      const buttonHandle = await page.evaluateHandle(
+        // @ts-expect-error button is expected to be in the page's scope.
+        () => button
+      );
+      // TODO (@jackfranklin): TS types are off here. evaluateHandle returns a
+      // JSHandle but that doesn't have a click() method. In this case it seems
+      // to return an ElementHandle. I'm not sure if the tests are wrong here
+      // and should use evaluate<ElementHandle> or if the type of evaluateHandle
+      // should change to enable the user to tell us they are expecting an
+      // ElementHandle rather than the default JSHandle.
+      await (buttonHandle as ElementHandle).click();
+      expect(
+        await page.evaluate(
+          // @ts-expect-error clicked is expected to be in the page's scope.
+          () => clicked
+        )
+      ).toBe(true);
     });
     it('should work for TextNodes', async () => {
       const { page, server } = getTestState();
@@ -195,6 +208,7 @@ describe('ElementHandle specs', function () {
         () => document.querySelector('button').firstChild
       );
       let error = null;
+      // @ts-expect-error
       await buttonTextNode.click().catch((error_) => (error = error_));
       expect(error.message).toBe('Node is not of type HTMLElement');
     });
@@ -293,7 +307,7 @@ describe('ElementHandle specs', function () {
       puppeteer.__experimental_unregisterCustomQueryHandler('getById');
       try {
         await page.$('getById/foo');
-        expect.fail('Custom query handler not set - throw expected');
+        throw new Error('Custom query handler name not set - throw expected');
       } catch (error) {
         expect(error).toStrictEqual(
           new Error(
@@ -307,9 +321,12 @@ describe('ElementHandle specs', function () {
         const { puppeteer } = getTestState();
         puppeteer.__experimental_registerCustomQueryHandler(
           '1/2/3',
-          (element, selector) => {}
+          // @ts-expect-error
+          () => {}
+        );
+        throw new Error(
+          'Custom query handler name was invalid - throw expected'
         );
-        expect.fail('Custom query handler name was invalid - throw expected');
       } catch (error) {
         expect(error).toStrictEqual(
           new Error('Custom query handler names may only contain [a-zA-Z]')
diff --git a/test/emulation.spec.js b/test/emulation.spec.ts
similarity index 90%
rename from test/emulation.spec.js
rename to test/emulation.spec.ts
index 6a1466519c4d2..d3b2b0ae48e5a 100644
--- a/test/emulation.spec.js
+++ b/test/emulation.spec.ts
@@ -14,12 +14,14 @@
  * limitations under the License.
  */
 
-const expect = require('expect');
-const {
+import expect from 'expect';
+import {
   getTestState,
   setupTestBrowserHooks,
   setupTestPageAndContextHooks,
-} = require('./mocha-utils');
+  itFailsFirefox,
+  describeFailsFirefox,
+} from './mocha-utils';
 
 describe('Emulation', () => {
   setupTestBrowserHooks();
@@ -95,7 +97,9 @@ describe('Emulation', () => {
 
         await page.setViewport({ width: 800, height: 600, hasTouch: true });
         await page.addScriptTag({ url: server.PREFIX + '/modernizr.js' });
-        expect(await page.evaluate(() => Modernizr.touchevents)).toBe(true);
+        expect(
+          await page.evaluate(() => globalThis.Modernizr.touchevents)
+        ).toBe(true);
       }
     );
     itFailsFirefox('should support landscape emulation', async () => {
@@ -138,7 +142,7 @@ describe('Emulation', () => {
         button
       );
       await button.click();
-      expect(await page.evaluate(() => result)).toBe('Clicked');
+      expect(await page.evaluate(() => globalThis.result)).toBe('Clicked');
     });
   });
 
@@ -162,11 +166,13 @@ describe('Emulation', () => {
       expect(await page.evaluate(() => matchMedia('print').matches)).toBe(
         false
       );
+      // @ts-expect-error this method is deprecated so we don't declare it
       await page.emulateMedia('print');
       expect(await page.evaluate(() => matchMedia('screen').matches)).toBe(
         false
       );
       expect(await page.evaluate(() => matchMedia('print').matches)).toBe(true);
+      // @ts-expect-error this method is deprecated so we don't declare it
       await page.emulateMedia(null);
       expect(await page.evaluate(() => matchMedia('screen').matches)).toBe(
         true
@@ -179,6 +185,7 @@ describe('Emulation', () => {
       const { page } = getTestState();
 
       let error = null;
+      // @ts-expect-error this method is deprecated so we don't declare it
       await page.emulateMedia('bad').catch((error_) => (error = error_));
       expect(error.message).toBe('Unsupported media type: bad');
     });
@@ -306,22 +313,22 @@ describe('Emulation', () => {
         globalThis.date = new Date(1479579154987);
       });
       await page.emulateTimezone('America/Jamaica');
-      expect(await page.evaluate(() => date.toString())).toBe(
+      expect(await page.evaluate(() => globalThis.date.toString())).toBe(
         'Sat Nov 19 2016 13:12:34 GMT-0500 (Eastern Standard Time)'
       );
 
       await page.emulateTimezone('Pacific/Honolulu');
-      expect(await page.evaluate(() => date.toString())).toBe(
+      expect(await page.evaluate(() => globalThis.date.toString())).toBe(
         'Sat Nov 19 2016 08:12:34 GMT-1000 (Hawaii-Aleutian Standard Time)'
       );
 
       await page.emulateTimezone('America/Buenos_Aires');
-      expect(await page.evaluate(() => date.toString())).toBe(
+      expect(await page.evaluate(() => globalThis.date.toString())).toBe(
         'Sat Nov 19 2016 15:12:34 GMT-0300 (Argentina Standard Time)'
       );
 
       await page.emulateTimezone('Europe/Berlin');
-      expect(await page.evaluate(() => date.toString())).toBe(
+      expect(await page.evaluate(() => globalThis.date.toString())).toBe(
         'Sat Nov 19 2016 19:12:34 GMT+0100 (Central European Standard Time)'
       );
     });
@@ -347,42 +354,49 @@ describe('Emulation', () => {
       {
         await page.emulateVisionDeficiency('none');
         const screenshot = await page.screenshot();
+        // @ts-expect-error TODO (@jackfranklin) toBeGolden needs declaring
         expect(screenshot).toBeGolden('screenshot-sanity.png');
       }
 
       {
         await page.emulateVisionDeficiency('achromatopsia');
         const screenshot = await page.screenshot();
+        // @ts-expect-error TODO (@jackfranklin) toBeGolden needs declaring
         expect(screenshot).toBeGolden('vision-deficiency-achromatopsia.png');
       }
 
       {
         await page.emulateVisionDeficiency('blurredVision');
         const screenshot = await page.screenshot();
+        // @ts-expect-error TODO (@jackfranklin) toBeGolden needs declaring
         expect(screenshot).toBeGolden('vision-deficiency-blurredVision.png');
       }
 
       {
         await page.emulateVisionDeficiency('deuteranopia');
         const screenshot = await page.screenshot();
+        // @ts-expect-error TODO (@jackfranklin) toBeGolden needs declaring
         expect(screenshot).toBeGolden('vision-deficiency-deuteranopia.png');
       }
 
       {
         await page.emulateVisionDeficiency('protanopia');
         const screenshot = await page.screenshot();
+        // @ts-expect-error TODO (@jackfranklin) toBeGolden needs declaring
         expect(screenshot).toBeGolden('vision-deficiency-protanopia.png');
       }
 
       {
         await page.emulateVisionDeficiency('tritanopia');
         const screenshot = await page.screenshot();
+        // @ts-expect-error TODO (@jackfranklin) toBeGolden needs declaring
         expect(screenshot).toBeGolden('vision-deficiency-tritanopia.png');
       }
 
       {
         await page.emulateVisionDeficiency('none');
         const screenshot = await page.screenshot();
+        // @ts-expect-error TODO (@jackfranklin) toBeGolden needs declaring
         expect(screenshot).toBeGolden('screenshot-sanity.png');
       }
     });
@@ -392,6 +406,7 @@ describe('Emulation', () => {
 
       let error = null;
       await page
+        // @ts-expect-error deliberately passign invalid deficiency
         .emulateVisionDeficiency('invalid')
         .catch((error_) => (error = error_));
       expect(error.message).toBe('Unsupported vision deficiency: invalid');
diff --git a/test/evaluation.spec.js b/test/evaluation.spec.ts
similarity index 92%
rename from test/evaluation.spec.js
rename to test/evaluation.spec.ts
index 2d870583ad901..a6e1cec95aa1c 100644
--- a/test/evaluation.spec.js
+++ b/test/evaluation.spec.ts
@@ -14,13 +14,15 @@
  * limitations under the License.
  */
 
-const utils = require('./utils');
-const expect = require('expect');
-const {
+import utils from './utils';
+import expect from 'expect';
+import {
   getTestState,
   setupTestBrowserHooks,
   setupTestPageAndContextHooks,
-} = require('./mocha-utils');
+  itFailsFirefox,
+  describeFailsFirefox,
+} from './mocha-utils';
 
 const bigint = typeof BigInt !== 'undefined';
 
@@ -80,7 +82,7 @@ describe('Evaluation specs', function () {
     it('should modify global environment', async () => {
       const { page } = getTestState();
 
-      await page.evaluate(() => (window.globalVar = 123));
+      await page.evaluate(() => (globalThis.globalVar = 123));
       expect(await page.evaluate('globalVar')).toBe(123);
     });
     it('should evaluate in the page context', async () => {
@@ -156,7 +158,7 @@ describe('Evaluation specs', function () {
         return await page.evaluate((a, b) => a * b, a, b);
       });
       const result = await page.evaluate(async function () {
-        return await callController(9, 3);
+        return await globalThis.callController(9, 3);
       });
       expect(result).toBe(27);
     });
@@ -165,10 +167,11 @@ describe('Evaluation specs', function () {
 
       let error = null;
       await page
-        .evaluate(() => not_existing_object.property)
+        // @ts-expect-error we know the object doesn't exist
+        .evaluate(() => notExistingObject.property)
         .catch((error_) => (error = error_));
       expect(error).toBeTruthy();
-      expect(error.message).toContain('not_existing_object');
+      expect(error.message).toContain('notExistingObject');
     });
     it('should support thrown strings as error messages', async () => {
       const { page } = getTestState();
@@ -259,7 +262,7 @@ describe('Evaluation specs', function () {
       const { page } = getTestState();
 
       const result = await page.evaluate(() => {
-        const a = {};
+        const a: { [x: string]: any } = {};
         const b = { a };
         a.b = b;
         return a;
@@ -274,7 +277,7 @@ describe('Evaluation specs', function () {
         .jsonValue()
         .catch((error_) => error_.message);
       const error = await page
-        .evaluate((errorText) => {
+        .evaluate<Error>((errorText) => {
           throw new Error(errorText);
         }, errorText)
         .catch((error_) => error_);
@@ -358,7 +361,7 @@ describe('Evaluation specs', function () {
       const error = await executionContext
         .evaluate(() => null)
         .catch((error_) => error_);
-      expect(error.message).toContain('navigation');
+      expect((error as Error).message).toContain('navigation');
     });
     itFailsFirefox(
       'should not throw an error when evaluation does a navigation',
@@ -367,7 +370,7 @@ describe('Evaluation specs', function () {
 
         await page.goto(server.PREFIX + '/one-style.html');
         const result = await page.evaluate(() => {
-          window.location = '/empty.html';
+          (window as any).location = '/empty.html';
           return [42];
         });
         expect(result).toEqual([42]);
@@ -376,7 +379,7 @@ describe('Evaluation specs', function () {
     it('should transfer 100Mb of data from page to node.js', async function () {
       const { page } = getTestState();
 
-      const a = await page.evaluate(() =>
+      const a = await page.evaluate<any[]>(() =>
         Array(100 * 1024 * 1024 + 1).join('a')
       );
       expect(a.length).toBe(100 * 1024 * 1024);
@@ -402,26 +405,26 @@ describe('Evaluation specs', function () {
       const { page, server } = getTestState();
 
       await page.evaluateOnNewDocument(function () {
-        window.injected = 123;
+        globalThis.injected = 123;
       });
       await page.goto(server.PREFIX + '/tamperable.html');
-      expect(await page.evaluate(() => window.result)).toBe(123);
+      expect(await page.evaluate(() => globalThis.result)).toBe(123);
     });
     it('should work with CSP', async () => {
       const { page, server } = getTestState();
 
       server.setCSP('/empty.html', 'script-src ' + server.PREFIX);
       await page.evaluateOnNewDocument(function () {
-        window.injected = 123;
+        globalThis.injected = 123;
       });
       await page.goto(server.PREFIX + '/empty.html');
-      expect(await page.evaluate(() => window.injected)).toBe(123);
+      expect(await page.evaluate(() => globalThis.injected)).toBe(123);
 
       // Make sure CSP works.
       await page
         .addScriptTag({ content: 'window.e = 10;' })
         .catch((error) => void error);
-      expect(await page.evaluate(() => window.e)).toBe(undefined);
+      expect(await page.evaluate(() => (window as any).e)).toBe(undefined);
     });
   });
 
@@ -432,10 +435,10 @@ describe('Evaluation specs', function () {
       await page.goto(server.EMPTY_PAGE);
       await utils.attachFrame(page, 'frame1', server.EMPTY_PAGE);
       expect(page.frames().length).toBe(2);
-      await page.frames()[0].evaluate(() => (window.FOO = 'foo'));
-      await page.frames()[1].evaluate(() => (window.FOO = 'bar'));
-      expect(await page.frames()[0].evaluate(() => window.FOO)).toBe('foo');
-      expect(await page.frames()[1].evaluate(() => window.FOO)).toBe('bar');
+      await page.frames()[0].evaluate(() => (globalThis.FOO = 'foo'));
+      await page.frames()[1].evaluate(() => (globalThis.FOO = 'bar'));
+      expect(await page.frames()[0].evaluate(() => globalThis.FOO)).toBe('foo');
+      expect(await page.frames()[1].evaluate(() => globalThis.FOO)).toBe('bar');
     });
     itFailsFirefox('should have correct execution contexts', async () => {
       const { page, server } = getTestState();
diff --git a/test/fixtures.spec.js b/test/fixtures.spec.ts
similarity index 92%
rename from test/fixtures.spec.js
rename to test/fixtures.spec.ts
index cb577ad3c5fb1..8a45c103067f7 100644
--- a/test/fixtures.spec.js
+++ b/test/fixtures.spec.ts
@@ -14,10 +14,12 @@
  * limitations under the License.
  */
 
-const expect = require('expect');
-const { getTestState } = require('./mocha-utils');
+/* eslint-disable @typescript-eslint/no-var-requires */
 
-const path = require('path');
+import expect from 'expect';
+import { getTestState, itChromeOnly } from './mocha-utils';
+
+import path from 'path';
 
 describe('Fixtures', function () {
   itChromeOnly('dumpio option should work with pipe option ', async () => {
@@ -67,7 +69,9 @@ describe('Fixtures', function () {
       JSON.stringify(options),
     ]);
     let wsEndPointCallback;
-    const wsEndPointPromise = new Promise((x) => (wsEndPointCallback = x));
+    const wsEndPointPromise = new Promise<string>(
+      (x) => (wsEndPointCallback = x)
+    );
     let output = '';
     res.stdout.on('data', (data) => {
       output += data;
diff --git a/test/frame.spec.js b/test/frame.spec.ts
similarity index 93%
rename from test/frame.spec.js
rename to test/frame.spec.ts
index 147c0629e330b..0e51db85be132 100644
--- a/test/frame.spec.js
+++ b/test/frame.spec.ts
@@ -14,13 +14,14 @@
  * limitations under the License.
  */
 
-const utils = require('./utils');
-const expect = require('expect');
-const {
+import utils from './utils';
+import expect from 'expect';
+import {
   getTestState,
   setupTestBrowserHooks,
   setupTestPageAndContextHooks,
-} = require('./mocha-utils');
+  itFailsFirefox,
+} from './mocha-utils';
 
 describe('Frame specs', function () {
   setupTestBrowserHooks();
@@ -43,12 +44,12 @@ describe('Frame specs', function () {
       expect(context2.frame()).toBe(frame2);
 
       await Promise.all([
-        context1.evaluate(() => (window.a = 1)),
-        context2.evaluate(() => (window.a = 2)),
+        context1.evaluate(() => (globalThis.a = 1)),
+        context2.evaluate(() => (globalThis.a = 2)),
       ]);
       const [a1, a2] = await Promise.all([
-        context1.evaluate(() => window.a),
-        context2.evaluate(() => window.a),
+        context1.evaluate(() => globalThis.a),
+        context2.evaluate(() => globalThis.a),
       ]);
       expect(a1).toBe(1);
       expect(a2).toBe(2);
@@ -146,8 +147,8 @@ describe('Frame specs', function () {
       const { page, server } = getTestState();
 
       let hasEvents = false;
-      page.on('frameattached', (frame) => (hasEvents = true));
-      page.on('framedetached', (frame) => (hasEvents = true));
+      page.on('frameattached', () => (hasEvents = true));
+      page.on('framedetached', () => (hasEvents = true));
       await page.goto(server.EMPTY_PAGE);
       expect(hasEvents).toBe(false);
     });
@@ -243,13 +244,13 @@ describe('Frame specs', function () {
           server.EMPTY_PAGE
         );
         await page.evaluate(() => {
-          window.frame = document.querySelector('#frame1');
-          window.frame.remove();
+          globalThis.frame = document.querySelector('#frame1');
+          globalThis.frame.remove();
         });
         expect(frame1.isDetached()).toBe(true);
         const [frame2] = await Promise.all([
           utils.waitEvent(page, 'frameattached'),
-          page.evaluate(() => document.body.appendChild(window.frame)),
+          page.evaluate(() => document.body.appendChild(globalThis.frame)),
         ]);
         expect(frame2.isDetached()).toBe(false);
         expect(frame1).not.toBe(frame2);
diff --git a/test/golden-utils.js b/test/golden-utils.js
index c8ac32b849ec6..f820afe6bfbb7 100644
--- a/test/golden-utils.js
+++ b/test/golden-utils.js
@@ -1,3 +1,4 @@
+// @ts-nocheck
 /**
  * Copyright 2017 Google Inc. All rights reserved.
  *
diff --git a/test/headful.spec.js b/test/headful.spec.ts
similarity index 93%
rename from test/headful.spec.js
rename to test/headful.spec.ts
index 11e33a7dcf144..23bc4f86a76ed 100644
--- a/test/headful.spec.js
+++ b/test/headful.spec.ts
@@ -14,15 +14,19 @@
  * limitations under the License.
  */
 
-const path = require('path');
-const os = require('os');
-const fs = require('fs');
-const { promisify } = require('util');
-const { waitEvent } = require('./utils');
-const expect = require('expect');
-const { getTestState } = require('./mocha-utils');
-
-const rmAsync = promisify(require('rimraf'));
+import path from 'path';
+import os from 'os';
+import fs from 'fs';
+import { promisify } from 'util';
+import expect from 'expect';
+import {
+  getTestState,
+  describeChromeOnly,
+  itFailsWindowsUntilDate,
+} from './mocha-utils';
+import rimraf from 'rimraf';
+
+const rmAsync = promisify(rimraf);
 const mkdtempAsync = promisify(fs.mkdtemp);
 
 const TMP_FOLDER = path.join(os.tmpdir(), 'pptr_tmp_folder-');
@@ -77,7 +81,7 @@ describeChromeOnly('headful tests', function () {
       );
       const page = await backgroundPageTarget.page();
       expect(await page.evaluate(() => 2 * 3)).toBe(6);
-      expect(await page.evaluate(() => window.MAGIC)).toBe(42);
+      expect(await page.evaluate(() => globalThis.MAGIC)).toBe(42);
       await browserWithExtension.close();
     });
     it('should have default url when launching browser', async function () {
@@ -120,13 +124,13 @@ describeChromeOnly('headful tests', function () {
         const cookie = await headlessPage.evaluate(() => document.cookie);
         await headlessBrowser.close();
         // This might throw. See https://github.com/puppeteer/puppeteer/issues/2778
-        await rmAsync(userDataDir).catch((error) => {});
+        await rmAsync(userDataDir).catch(() => {});
         expect(cookie).toBe('foo=true');
       }
     );
     // TODO: Support OOOPIF. @see https://github.com/puppeteer/puppeteer/issues/2548
     xit('OOPIF: should report google.com frame', async () => {
-      const { server } = getTestState();
+      const { server, puppeteer } = getTestState();
 
       // https://google.com is isolated by default in Chromium embedder.
       const browser = await puppeteer.launch(headfulOptions);
diff --git a/test/ignorehttpserrors.spec.js b/test/ignorehttpserrors.spec.ts
similarity index 97%
rename from test/ignorehttpserrors.spec.js
rename to test/ignorehttpserrors.spec.ts
index 170088ae270df..1532ee6b4b978 100644
--- a/test/ignorehttpserrors.spec.js
+++ b/test/ignorehttpserrors.spec.ts
@@ -14,8 +14,12 @@
  * limitations under the License.
  */
 
-const expect = require('expect');
-const { getTestState } = require('./mocha-utils');
+import expect from 'expect';
+import {
+  getTestState,
+  describeFailsFirefox,
+  itFailsFirefox,
+} from './mocha-utils';
 
 describe('ignoreHTTPSErrors', function () {
   /* Note that this test creates its own browser rather than use
diff --git a/test/input.spec.js b/test/input.spec.ts
similarity index 96%
rename from test/input.spec.js
rename to test/input.spec.ts
index 8094737da6cf8..5bf1e76e54609 100644
--- a/test/input.spec.js
+++ b/test/input.spec.ts
@@ -14,13 +14,14 @@
  * limitations under the License.
  */
 
-const path = require('path');
-const expect = require('expect');
-const {
+import path from 'path';
+import expect from 'expect';
+import {
   getTestState,
   setupTestBrowserHooks,
   setupTestPageAndContextHooks,
-} = require('./mocha-utils');
+  describeFailsFirefox,
+} from './mocha-utils';
 
 const FILE_TO_UPLOAD = path.join(__dirname, '/assets/file-to-upload.txt');
 
@@ -36,9 +37,13 @@ describe('input tests', function () {
       const filePath = path.relative(process.cwd(), FILE_TO_UPLOAD);
       const input = await page.$('input');
       await page.evaluate((e) => {
-        window._inputEvents = [];
-        e.addEventListener('change', (ev) => window._inputEvents.push(ev.type));
-        e.addEventListener('input', (ev) => window._inputEvents.push(ev.type));
+        globalThis._inputEvents = [];
+        e.addEventListener('change', (ev) =>
+          globalThis._inputEvents.push(ev.type)
+        );
+        e.addEventListener('input', (ev) =>
+          globalThis._inputEvents.push(ev.type)
+        );
       }, input);
       await input.uploadFile(filePath);
       expect(await page.evaluate((e) => e.files[0].name, input)).toBe(
@@ -47,7 +52,7 @@ describe('input tests', function () {
       expect(await page.evaluate((e) => e.files[0].type, input)).toBe(
         'text/plain'
       );
-      expect(await page.evaluate(() => window._inputEvents)).toEqual([
+      expect(await page.evaluate(() => globalThis._inputEvents)).toEqual([
         'input',
         'change',
       ]);
diff --git a/test/jshandle.spec.js b/test/jshandle.spec.ts
similarity index 95%
rename from test/jshandle.spec.js
rename to test/jshandle.spec.ts
index 7542af3d0aaea..f684776fb9d84 100644
--- a/test/jshandle.spec.js
+++ b/test/jshandle.spec.ts
@@ -14,12 +14,13 @@
  * limitations under the License.
  */
 
-const expect = require('expect');
-const {
+import expect from 'expect';
+import {
   getTestState,
   setupTestBrowserHooks,
   setupTestPageAndContextHooks,
-} = require('./mocha-utils');
+  itFailsFirefox,
+} from './mocha-utils';
 
 describe('JSHandle', function () {
   setupTestBrowserHooks();
@@ -70,7 +71,7 @@ describe('JSHandle', function () {
       const { page } = getTestState();
 
       const aHandle = await page.evaluateHandle(() => {
-        window.FOO = 123;
+        globalThis.FOO = 123;
         return window;
       });
       expect(await page.evaluate((e) => e.FOO, aHandle)).toBe(123);
@@ -79,7 +80,7 @@ describe('JSHandle', function () {
       const { page } = getTestState();
 
       const aHandle = await page.evaluateHandle(() => {
-        window.FOO = 123;
+        globalThis.FOO = 123;
         return window;
       });
       expect(await page.evaluate((e) => e.FOO, aHandle)).toBe(123);
@@ -146,11 +147,13 @@ describe('JSHandle', function () {
 
       const aHandle = await page.evaluateHandle(() => {
         class A {
+          a: string;
           constructor() {
             this.a = '1';
           }
         }
         class B extends A {
+          b: string;
           constructor() {
             super();
             this.b = '2';
@@ -189,17 +192,15 @@ describe('JSHandle', function () {
       const element = aHandle.asElement();
       expect(element).toBeTruthy();
       expect(
-        await page.evaluate(
-          (e) => e.nodeType === HTMLElement.TEXT_NODE,
-          element
-        )
+        await page.evaluate((e) => e.nodeType === Node.TEXT_NODE, element)
       );
     });
     it('should work with nullified Node', async () => {
       const { page } = getTestState();
 
       await page.setContent('<section>test</section>');
-      await page.evaluate(() => delete Node);
+      // TODO (@jackfranklin): this line doesn't do anything. What was intended here?
+      // await page.evaluate(() => delete Node);
       const handle = await page.evaluateHandle(() =>
         document.querySelector('section')
       );
diff --git a/test/keyboard.spec.js b/test/keyboard.spec.ts
similarity index 83%
rename from test/keyboard.spec.js
rename to test/keyboard.spec.ts
index 03be64d73828e..abf31e64826ed 100644
--- a/test/keyboard.spec.js
+++ b/test/keyboard.spec.ts
@@ -14,14 +14,16 @@
  * limitations under the License.
  */
 
-const utils = require('./utils');
-const os = require('os');
-const expect = require('expect');
-const {
+import utils from './utils';
+import os from 'os';
+import expect from 'expect';
+import {
   getTestState,
   setupTestBrowserHooks,
   setupTestPageAndContextHooks,
-} = require('./mocha-utils');
+  itFailsFirefox,
+} from './mocha-utils';
+import { KeyInput } from '../src/common/USKeyboardLayout';
 
 describe('Keyboard', function () {
   setupTestBrowserHooks();
@@ -45,7 +47,7 @@ describe('Keyboard', function () {
     const { page, isFirefox } = getTestState();
 
     await page.evaluate(() => {
-      window.keyPromise = new Promise((resolve) =>
+      (window as any).keyPromise = new Promise((resolve) =>
         document.addEventListener('keydown', (event) => resolve(event.key))
       );
     });
@@ -130,16 +132,20 @@ describe('Keyboard', function () {
 
     await page.goto(server.PREFIX + '/input/keyboard.html');
     const keyboard = page.keyboard;
-    const codeForKey = { Shift: 16, Alt: 18, Control: 17 };
-    for (const modifierKey in codeForKey) {
+    const codeForKey = new Map<KeyInput, number>([
+      ['Shift', 16],
+      ['Alt', 18],
+      ['Control', 17],
+    ]);
+    for (const [modifierKey, modifierCode] of codeForKey) {
       await keyboard.down(modifierKey);
-      expect(await page.evaluate(() => getResult())).toBe(
+      expect(await page.evaluate(() => globalThis.getResult())).toBe(
         'Keydown: ' +
           modifierKey +
           ' ' +
           modifierKey +
           'Left ' +
-          codeForKey[modifierKey] +
+          modifierCode +
           ' [' +
           modifierKey +
           ']'
@@ -147,7 +153,7 @@ describe('Keyboard', function () {
       await keyboard.down('!');
       // Shift+! will generate a keypress
       if (modifierKey === 'Shift')
-        expect(await page.evaluate(() => getResult())).toBe(
+        expect(await page.evaluate(() => globalThis.getResult())).toBe(
           'Keydown: ! Digit1 49 [' +
             modifierKey +
             ']\nKeypress: ! Digit1 33 33 [' +
@@ -155,22 +161,22 @@ describe('Keyboard', function () {
             ']'
         );
       else
-        expect(await page.evaluate(() => getResult())).toBe(
+        expect(await page.evaluate(() => globalThis.getResult())).toBe(
           'Keydown: ! Digit1 49 [' + modifierKey + ']'
         );
 
       await keyboard.up('!');
-      expect(await page.evaluate(() => getResult())).toBe(
+      expect(await page.evaluate(() => globalThis.getResult())).toBe(
         'Keyup: ! Digit1 49 [' + modifierKey + ']'
       );
       await keyboard.up(modifierKey);
-      expect(await page.evaluate(() => getResult())).toBe(
+      expect(await page.evaluate(() => globalThis.getResult())).toBe(
         'Keyup: ' +
           modifierKey +
           ' ' +
           modifierKey +
           'Left ' +
-          codeForKey[modifierKey] +
+          modifierCode +
           ' []'
       );
     }
@@ -181,27 +187,27 @@ describe('Keyboard', function () {
     await page.goto(server.PREFIX + '/input/keyboard.html');
     const keyboard = page.keyboard;
     await keyboard.down('Control');
-    expect(await page.evaluate(() => getResult())).toBe(
+    expect(await page.evaluate(() => globalThis.getResult())).toBe(
       'Keydown: Control ControlLeft 17 [Control]'
     );
     await keyboard.down('Alt');
-    expect(await page.evaluate(() => getResult())).toBe(
+    expect(await page.evaluate(() => globalThis.getResult())).toBe(
       'Keydown: Alt AltLeft 18 [Alt Control]'
     );
     await keyboard.down(';');
-    expect(await page.evaluate(() => getResult())).toBe(
+    expect(await page.evaluate(() => globalThis.getResult())).toBe(
       'Keydown: ; Semicolon 186 [Alt Control]'
     );
     await keyboard.up(';');
-    expect(await page.evaluate(() => getResult())).toBe(
+    expect(await page.evaluate(() => globalThis.getResult())).toBe(
       'Keyup: ; Semicolon 186 [Alt Control]'
     );
     await keyboard.up('Control');
-    expect(await page.evaluate(() => getResult())).toBe(
+    expect(await page.evaluate(() => globalThis.getResult())).toBe(
       'Keyup: Control ControlLeft 17 [Alt]'
     );
     await keyboard.up('Alt');
-    expect(await page.evaluate(() => getResult())).toBe(
+    expect(await page.evaluate(() => globalThis.getResult())).toBe(
       'Keyup: Alt AltLeft 18 []'
     );
   });
@@ -210,7 +216,7 @@ describe('Keyboard', function () {
 
     await page.goto(server.PREFIX + '/input/keyboard.html');
     await page.keyboard.type('!');
-    expect(await page.evaluate(() => getResult())).toBe(
+    expect(await page.evaluate(() => globalThis.getResult())).toBe(
       [
         'Keydown: ! Digit1 49 []',
         'Keypress: ! Digit1 33 33 []',
@@ -218,7 +224,7 @@ describe('Keyboard', function () {
       ].join('\n')
     );
     await page.keyboard.type('^');
-    expect(await page.evaluate(() => getResult())).toBe(
+    expect(await page.evaluate(() => globalThis.getResult())).toBe(
       [
         'Keydown: ^ Digit6 54 []',
         'Keypress: ^ Digit6 94 94 []',
@@ -233,7 +239,7 @@ describe('Keyboard', function () {
     const keyboard = page.keyboard;
     await keyboard.down('Shift');
     await page.keyboard.type('~');
-    expect(await page.evaluate(() => getResult())).toBe(
+    expect(await page.evaluate(() => globalThis.getResult())).toBe(
       [
         'Keydown: Shift ShiftLeft 16 [Shift]',
         'Keydown: ~ Backquote 192 [Shift]', // 192 is ` keyCode
@@ -261,7 +267,9 @@ describe('Keyboard', function () {
       );
     });
     await page.keyboard.type('Hello World!');
-    expect(await page.evaluate(() => textarea.value)).toBe('He Wrd!');
+    expect(await page.evaluate(() => globalThis.textarea.value)).toBe(
+      'He Wrd!'
+    );
   });
   itFailsFirefox('should specify repeat property', async () => {
     const { page, server } = getTestState();
@@ -271,21 +279,21 @@ describe('Keyboard', function () {
     await page.evaluate(() =>
       document
         .querySelector('textarea')
-        .addEventListener('keydown', (e) => (window.lastEvent = e), true)
+        .addEventListener('keydown', (e) => (globalThis.lastEvent = e), true)
     );
     await page.keyboard.down('a');
-    expect(await page.evaluate(() => window.lastEvent.repeat)).toBe(false);
+    expect(await page.evaluate(() => globalThis.lastEvent.repeat)).toBe(false);
     await page.keyboard.press('a');
-    expect(await page.evaluate(() => window.lastEvent.repeat)).toBe(true);
+    expect(await page.evaluate(() => globalThis.lastEvent.repeat)).toBe(true);
 
     await page.keyboard.down('b');
-    expect(await page.evaluate(() => window.lastEvent.repeat)).toBe(false);
+    expect(await page.evaluate(() => globalThis.lastEvent.repeat)).toBe(false);
     await page.keyboard.down('b');
-    expect(await page.evaluate(() => window.lastEvent.repeat)).toBe(true);
+    expect(await page.evaluate(() => globalThis.lastEvent.repeat)).toBe(true);
 
     await page.keyboard.up('a');
     await page.keyboard.down('a');
-    expect(await page.evaluate(() => window.lastEvent.repeat)).toBe(false);
+    expect(await page.evaluate(() => globalThis.lastEvent.repeat)).toBe(false);
   });
   itFailsFirefox('should type all kinds of characters', async () => {
     const { page, server } = getTestState();
@@ -303,7 +311,7 @@ describe('Keyboard', function () {
     await page.evaluate(() => {
       window.addEventListener(
         'keydown',
-        (event) => (window.keyLocation = event.location),
+        (event) => (globalThis.keyLocation = event.location),
         true
       );
     });
@@ -325,13 +333,16 @@ describe('Keyboard', function () {
     const { page } = getTestState();
 
     let error = await page.keyboard
+      // @ts-expect-error
       .press('NotARealKey')
       .catch((error_) => error_);
     expect(error.message).toBe('Unknown key: "NotARealKey"');
 
+    // @ts-expect-error
     error = await page.keyboard.press('ё').catch((error_) => error_);
     expect(error && error.message).toBe('Unknown key: "ё"');
 
+    // @ts-expect-error
     error = await page.keyboard.press('😊').catch((error_) => error_);
     expect(error && error.message).toBe('Unknown key: "😊"');
   });
@@ -364,9 +375,9 @@ describe('Keyboard', function () {
     const { page, isFirefox } = getTestState();
 
     await page.evaluate(() => {
-      window.result = null;
+      globalThis.result = null;
       document.addEventListener('keydown', (event) => {
-        window.result = [event.key, event.code, event.metaKey];
+        globalThis.result = [event.key, event.code, event.metaKey];
       });
     });
     await page.keyboard.press('Meta');
diff --git a/test/launcher.spec.js b/test/launcher.spec.ts
similarity index 96%
rename from test/launcher.spec.js
rename to test/launcher.spec.ts
index 7b470562092f4..bcb6cf2eb808e 100644
--- a/test/launcher.spec.js
+++ b/test/launcher.spec.ts
@@ -13,19 +13,27 @@
  * See the License for the specific language governing permissions and
  * limitations under the License.
  */
-const fs = require('fs');
-const os = require('os');
-const path = require('path');
-const sinon = require('sinon');
-const { helper } = require('../lib/common/helper');
-const rmAsync = helper.promisify(require('rimraf'));
+import fs from 'fs';
+import os from 'os';
+import path from 'path';
+import sinon from 'sinon';
+import { helper } from '../src/common/helper';
+import {
+  getTestState,
+  itFailsFirefox,
+  itOnlyRegularInstall,
+  itFailsWindowsUntilDate,
+} from './mocha-utils';
+import utils from './utils';
+import expect from 'expect';
+import rimraf from 'rimraf';
+import { Page } from '../src/common/Page';
+
+const rmAsync = helper.promisify(rimraf);
 const mkdtempAsync = helper.promisify(fs.mkdtemp);
 const readFileAsync = helper.promisify(fs.readFile);
 const statAsync = helper.promisify(fs.stat);
 const TMP_FOLDER = path.join(os.tmpdir(), 'pptr_tmp_folder-');
-const utils = require('./utils');
-const expect = require('expect');
-const { getTestState } = require('./mocha-utils');
 
 describe('Launcher specs', function () {
   if (getTestState().isFirefox) this.timeout(30 * 1000);
@@ -187,7 +195,7 @@ describe('Launcher specs', function () {
         const page = await browser.newPage();
         let error = null;
         const neverResolves = page
-          .evaluate(() => new Promise((r) => {}))
+          .evaluate(() => new Promise(() => {}))
           .catch((error_) => (error = error_));
         await browser.close();
         await neverResolves;
@@ -215,7 +223,7 @@ describe('Launcher specs', function () {
         await browser.close();
         expect(fs.readdirSync(userDataDir).length).toBeGreaterThan(0);
         // This might throw. See https://github.com/puppeteer/puppeteer/issues/2778
-        await rmAsync(userDataDir).catch((error) => {});
+        await rmAsync(userDataDir).catch(() => {});
       });
       it('userDataDir argument', async () => {
         const { isChrome, puppeteer, defaultBrowserOptions } = getTestState();
@@ -239,7 +247,7 @@ describe('Launcher specs', function () {
         await browser.close();
         expect(fs.readdirSync(userDataDir).length).toBeGreaterThan(0);
         // This might throw. See https://github.com/puppeteer/puppeteer/issues/2778
-        await rmAsync(userDataDir).catch((error) => {});
+        await rmAsync(userDataDir).catch(() => {});
       });
       it('userDataDir option should restore state', async () => {
         const { server, puppeteer, defaultBrowserOptions } = getTestState();
@@ -258,12 +266,12 @@ describe('Launcher specs', function () {
         expect(await page2.evaluate(() => localStorage.hey)).toBe('hello');
         await browser2.close();
         // This might throw. See https://github.com/puppeteer/puppeteer/issues/2778
-        await rmAsync(userDataDir).catch((error) => {});
+        await rmAsync(userDataDir).catch(() => {});
       });
       // This mysteriously fails on Windows on AppVeyor. See
       // https://github.com/puppeteer/puppeteer/issues/4111
       xit('userDataDir option should restore cookies', async () => {
-        const { server, puppeteer } = getTestState();
+        const { server, puppeteer, defaultBrowserOptions } = getTestState();
 
         const userDataDir = await mkdtempAsync(TMP_FOLDER);
         const options = Object.assign({ userDataDir }, defaultBrowserOptions);
@@ -285,7 +293,7 @@ describe('Launcher specs', function () {
         );
         await browser2.close();
         // This might throw. See https://github.com/puppeteer/puppeteer/issues/2778
-        await rmAsync(userDataDir).catch((error) => {});
+        await rmAsync(userDataDir).catch(() => {});
       });
       it('should return the default arguments', async () => {
         const { isChrome, isFirefox, puppeteer } = getTestState();
@@ -351,6 +359,9 @@ describe('Launcher specs', function () {
           })
         );
         const spawnargs = browser.process().spawnargs;
+        if (!spawnargs) {
+          throw new Error('spawnargs not present');
+        }
         expect(spawnargs.indexOf(defaultArgs[0])).toBe(-1);
         expect(spawnargs.indexOf(defaultArgs[1])).not.toBe(-1);
         expect(spawnargs.indexOf(defaultArgs[2])).toBe(-1);
@@ -486,10 +497,7 @@ describe('Launcher specs', function () {
         otherBrowser.disconnect();
 
         const secondPage = await originalBrowser.newPage();
-        expect(await secondPage.evaluate(() => 7 * 6)).toBe(
-          42,
-          'original browser should still work'
-        );
+        expect(await secondPage.evaluate(() => 7 * 6)).toBe(42);
         await originalBrowser.close();
       });
       it('should be able to close remote browser', async () => {
@@ -571,7 +579,7 @@ describe('Launcher specs', function () {
             browserWSEndpoint: browserOne.wsEndpoint(),
           });
           const [page1, page2] = await Promise.all([
-            new Promise((x) =>
+            new Promise<Page>((x) =>
               browserOne.once('targetcreated', (target) => x(target.page()))
             ),
             browserTwo.newPage(),
diff --git a/test/mocha-utils.js b/test/mocha-utils.ts
similarity index 65%
rename from test/mocha-utils.js
rename to test/mocha-utils.ts
index d72b180304439..982751fba1740 100644
--- a/test/mocha-utils.js
+++ b/test/mocha-utils.ts
@@ -14,16 +14,19 @@
  * limitations under the License.
  */
 
-const { TestServer } = require('../utils/testserver/index');
-const path = require('path');
-const fs = require('fs');
-const os = require('os');
-const sinon = require('sinon');
-const puppeteer = require('../');
-const utils = require('./utils');
-const rimraf = require('rimraf');
-
-const { trackCoverage } = require('./coverage-utils');
+import { TestServer } from '../utils/testserver/index';
+import * as path from 'path';
+import * as fs from 'fs';
+import * as os from 'os';
+import sinon from 'sinon';
+import puppeteer from '../src/index';
+import { Browser, BrowserContext } from '../src/common/Browser';
+import { Page } from '../src/common/Page';
+import { Puppeteer } from '../src/common/Puppeteer';
+import utils from './utils';
+import rimraf from 'rimraf';
+
+import { trackCoverage } from './coverage-utils';
 
 const setupServer = async () => {
   const assetsPath = path.join(__dirname, 'assets');
@@ -48,7 +51,8 @@ const setupServer = async () => {
   return { server, httpsServer };
 };
 
-exports.getTestState = () => state;
+export const getTestState = (): PuppeteerTestState =>
+  state as PuppeteerTestState;
 
 const product =
   process.env.PRODUCT || process.env.PUPPETEER_PRODUCT || 'Chromium';
@@ -73,19 +77,20 @@ const defaultBrowserOptions = Object.assign(
   {
     handleSIGINT: true,
     executablePath: process.env.BINARY,
-    slowMo: false,
     headless: isHeadless,
     dumpio: !!process.env.DUMPIO,
   },
   extraLaunchOptions
 );
 
-(async () => {
+(async (): Promise<void> => {
   if (defaultBrowserOptions.executablePath) {
     console.warn(
       `WARN: running ${product} tests with ${defaultBrowserOptions.executablePath}`
     );
   } else {
+    // TODO(jackfranklin): declare updateRevision in some form for the Firefox launcher.
+    // @ts-expect-error
     if (product === 'firefox') await puppeteer._launcher._updateRevision();
     const executablePath = puppeteer.executablePath();
     if (!fs.existsSync(executablePath))
@@ -95,7 +100,7 @@ const defaultBrowserOptions = Object.assign(
   }
 })();
 
-const setupGoldenAssertions = () => {
+const setupGoldenAssertions = (): void => {
   const suffix = product.toLowerCase();
   const GOLDEN_DIR = path.join(__dirname, 'golden-' + suffix);
   const OUTPUT_DIR = path.join(__dirname, 'output-' + suffix);
@@ -105,44 +110,78 @@ const setupGoldenAssertions = () => {
 
 setupGoldenAssertions();
 
-const state = {};
-
-global.itFailsFirefox = (...args) => {
-  if (isFirefox) return xit(...args);
-  else return it(...args);
+interface PuppeteerTestState {
+  browser: Browser;
+  context: BrowserContext;
+  page: Page;
+  puppeteer: Puppeteer;
+  defaultBrowserOptions: {
+    [x: string]: any;
+  };
+  server: any;
+  httpsServer: any;
+  isFirefox: boolean;
+  isChrome: boolean;
+  isHeadless: boolean;
+  puppeteerPath: string;
+}
+const state: Partial<PuppeteerTestState> = {};
+
+export const itFailsFirefox = (
+  description: string,
+  body: Mocha.Func
+): Mocha.Test => {
+  if (isFirefox) return xit(description, body);
+  else return it(description, body);
 };
 
-global.itChromeOnly = (...args) => {
-  if (isChrome) return it(...args);
-  else return xit(...args);
+export const itChromeOnly = (
+  description: string,
+  body: Mocha.Func
+): Mocha.Test => {
+  if (isChrome) return it(description, body);
+  else return xit(description, body);
 };
 
-global.itOnlyRegularInstall = (...args) => {
-  if (alternativeInstall || process.env.BINARY) return xit(...args);
-  else return it(...args);
+export const itOnlyRegularInstall = (
+  description: string,
+  body: Mocha.Func
+): Mocha.Test => {
+  if (alternativeInstall || process.env.BINARY) return xit(description, body);
+  else return it(description, body);
 };
 
-global.itFailsWindowsUntilDate = (date, ...args) => {
-  if (os.platform() === 'win32' && Date.now() < date) {
+export const itFailsWindowsUntilDate = (
+  date: Date,
+  description: string,
+  body: Mocha.Func
+): Mocha.Test => {
+  if (os.platform() === 'win32' && Date.now() < date.getTime()) {
     // we are within the deferred time so skip the test
-    return xit(...args);
+    return xit(description, body);
   }
 
-  return it(...args);
+  return it(description, body);
 };
 
-global.describeFailsFirefox = (...args) => {
-  if (isFirefox) return xdescribe(...args);
-  else return describe(...args);
+export const describeFailsFirefox = (
+  description: string,
+  body: (this: Mocha.Suite) => void
+): void | Mocha.Suite => {
+  if (isFirefox) return xdescribe(description, body);
+  else return describe(description, body);
 };
 
-global.describeChromeOnly = (...args) => {
-  if (isChrome) return describe(...args);
+export const describeChromeOnly = (
+  description: string,
+  body: (this: Mocha.Suite) => void
+): Mocha.Suite => {
+  if (isChrome) return describe(description, body);
 };
 
 let coverageHooks = {
-  beforeAll: () => {},
-  afterAll: () => {},
+  beforeAll: (): void => {},
+  afterAll: (): void => {},
 };
 
 if (process.env.COVERAGE) {
@@ -158,7 +197,7 @@ console.log(
   }`
 );
 
-exports.setupTestBrowserHooks = () => {
+export const setupTestBrowserHooks = () => {
   before(async () => {
     const browser = await puppeteer.launch(defaultBrowserOptions);
     state.browser = browser;
@@ -170,7 +209,7 @@ exports.setupTestBrowserHooks = () => {
   });
 };
 
-exports.setupTestPageAndContextHooks = () => {
+export const setupTestPageAndContextHooks = () => {
   beforeEach(async () => {
     state.context = await state.browser.createIncognitoBrowserContext();
     state.page = await state.context.newPage();
@@ -183,7 +222,7 @@ exports.setupTestPageAndContextHooks = () => {
   });
 };
 
-exports.mochaHooks = {
+export const mochaHooks = {
   beforeAll: [
     async () => {
       const { server, httpsServer } = await setupServer();
diff --git a/test/mouse.spec.js b/test/mouse.spec.ts
similarity index 82%
rename from test/mouse.spec.js
rename to test/mouse.spec.ts
index d46fb2f8caa9b..1cca238d71c23 100644
--- a/test/mouse.spec.js
+++ b/test/mouse.spec.ts
@@ -13,15 +13,24 @@
  * See the License for the specific language governing permissions and
  * limitations under the License.
  */
-const os = require('os');
-const expect = require('expect');
-const {
+import os from 'os';
+import expect from 'expect';
+import {
   getTestState,
   setupTestBrowserHooks,
   setupTestPageAndContextHooks,
-} = require('./mocha-utils');
+  itFailsFirefox,
+} from './mocha-utils';
+import { KeyInput } from '../src/common/USKeyboardLayout';
 
-function dimensions() {
+interface Dimensions {
+  x: number;
+  y: number;
+  width: number;
+  height: number;
+}
+
+function dimensions(): Dimensions {
   const rect = document.querySelector('textarea').getBoundingClientRect();
   return {
     x: rect.left,
@@ -38,7 +47,7 @@ describe('Mouse', function () {
     const { page } = getTestState();
 
     await page.evaluate(() => {
-      window.clickPromise = new Promise((resolve) => {
+      globalThis.clickPromise = new Promise((resolve) => {
         document.addEventListener('click', (event) => {
           resolve({
             type: event.type,
@@ -52,7 +61,9 @@ describe('Mouse', function () {
       });
     });
     await page.mouse.click(50, 60);
-    const event = await page.evaluate(() => window.clickPromise);
+    const event = await page.evaluate<MouseEvent>(
+      () => globalThis.clickPromise
+    );
     expect(event.type).toBe('click');
     expect(event.detail).toBe(1);
     expect(event.clientX).toBe(50);
@@ -64,13 +75,13 @@ describe('Mouse', function () {
     const { page, server } = getTestState();
 
     await page.goto(server.PREFIX + '/input/textarea.html');
-    const { x, y, width, height } = await page.evaluate(dimensions);
+    const { x, y, width, height } = await page.evaluate<Dimensions>(dimensions);
     const mouse = page.mouse;
     await mouse.move(x + width - 4, y + height - 4);
     await mouse.down();
     await mouse.move(x + width + 100, y + height + 100);
     await mouse.up();
-    const newDimensions = await page.evaluate(dimensions);
+    const newDimensions = await page.evaluate<Dimensions>(dimensions);
     expect(newDimensions.width).toBe(Math.round(width + 104));
     expect(newDimensions.height).toBe(Math.round(height + 104));
   });
@@ -139,33 +150,26 @@ describe('Mouse', function () {
     await page.evaluate(() =>
       document
         .querySelector('#button-3')
-        .addEventListener('mousedown', (e) => (window.lastEvent = e), true)
+        .addEventListener('mousedown', (e) => (globalThis.lastEvent = e), true)
     );
-    const modifiers = {
-      Shift: 'shiftKey',
-      Control: 'ctrlKey',
-      Alt: 'altKey',
-      Meta: 'metaKey',
-    };
+    const modifiers = new Map<KeyInput, string>([
+      ['Shift', 'shiftKey'],
+      ['Control', 'ctrlKey'],
+      ['Alt', 'altKey'],
+      ['Meta', 'metaKey'],
+    ]);
     // In Firefox, the Meta modifier only exists on Mac
     if (isFirefox && os.platform() !== 'darwin') delete modifiers['Meta'];
-    for (const modifier in modifiers) {
+    for (const [modifier, key] of modifiers) {
       await page.keyboard.down(modifier);
       await page.click('#button-3');
-      if (
-        !(await page.evaluate(
-          (mod) => window.lastEvent[mod],
-          modifiers[modifier]
-        ))
-      )
-        throw new Error(modifiers[modifier] + ' should be true');
+      if (!(await page.evaluate((mod) => globalThis.lastEvent[mod], key)))
+        throw new Error(key + ' should be true');
       await page.keyboard.up(modifier);
     }
     await page.click('#button-3');
-    for (const modifier in modifiers) {
-      if (
-        await page.evaluate((mod) => window.lastEvent[mod], modifiers[modifier])
-      )
+    for (const [modifier, key] of modifiers) {
+      if (await page.evaluate((mod) => globalThis.lastEvent[mod], key))
         throw new Error(modifiers[modifier] + ' should be false');
     }
   });
@@ -174,9 +178,9 @@ describe('Mouse', function () {
 
     await page.mouse.move(100, 100);
     await page.evaluate(() => {
-      window.result = [];
+      globalThis.result = [];
       document.addEventListener('mousemove', (event) => {
-        window.result.push([event.clientX, event.clientY]);
+        globalThis.result.push([event.clientX, event.clientY]);
       });
     });
     await page.mouse.move(200, 300, { steps: 5 });
@@ -199,7 +203,7 @@ describe('Mouse', function () {
       await page.goto(server.CROSS_PROCESS_PREFIX + '/mobile.html');
       await page.evaluate(() => {
         document.addEventListener('click', (event) => {
-          window.result = { x: event.clientX, y: event.clientY };
+          globalThis.result = { x: event.clientX, y: event.clientY };
         });
       });
 
diff --git a/test/navigation.spec.js b/test/navigation.spec.ts
similarity index 96%
rename from test/navigation.spec.js
rename to test/navigation.spec.ts
index 330d8d0d89137..6475ef2ded388 100644
--- a/test/navigation.spec.js
+++ b/test/navigation.spec.ts
@@ -14,14 +14,16 @@
  * limitations under the License.
  */
 
-const utils = require('./utils');
-const expect = require('expect');
-const {
+import utils from './utils';
+import expect from 'expect';
+import {
   getTestState,
   setupTestBrowserHooks,
   setupTestPageAndContextHooks,
-} = require('./mocha-utils');
-const os = require('os');
+  itFailsFirefox,
+  describeFailsFirefox,
+} from './mocha-utils';
+import os from 'os';
 
 describe('navigation', function () {
   setupTestBrowserHooks();
@@ -155,9 +157,9 @@ describe('navigation', function () {
       // Make sure that network events do not emit 'undefined'.
       // @see https://crbug.com/750469
       const requests = [];
-      page.on('request', (request) => requests.push('request'));
-      page.on('requestfinished', (request) => requests.push('requestfinished'));
-      page.on('requestfailed', (request) => requests.push('requestfailed'));
+      page.on('request', () => requests.push('request'));
+      page.on('requestfinished', () => requests.push('requestfinished'));
+      page.on('requestfailed', () => requests.push('requestfailed'));
 
       let error = null;
       await page
@@ -187,6 +189,7 @@ describe('navigation', function () {
 
       let error = null;
       await page
+        // @ts-expect-error
         .goto(server.EMPTY_PAGE, { waitUntil: 'networkidle' })
         .catch((error_) => (error = error_));
       expect(error.message).toContain(
@@ -208,7 +211,7 @@ describe('navigation', function () {
       const { page, server, puppeteer } = getTestState();
 
       // Hang for request to the empty.html
-      server.setRoute('/empty.html', (req, res) => {});
+      server.setRoute('/empty.html', () => {});
       let error = null;
       await page
         .goto(server.PREFIX + '/empty.html', { timeout: 1 })
@@ -220,7 +223,7 @@ describe('navigation', function () {
       const { page, server, puppeteer } = getTestState();
 
       // Hang for request to the empty.html
-      server.setRoute('/empty.html', (req, res) => {});
+      server.setRoute('/empty.html', () => {});
       let error = null;
       page.setDefaultNavigationTimeout(1);
       await page
@@ -233,7 +236,7 @@ describe('navigation', function () {
       const { page, server, puppeteer } = getTestState();
 
       // Hang for request to the empty.html
-      server.setRoute('/empty.html', (req, res) => {});
+      server.setRoute('/empty.html', () => {});
       let error = null;
       page.setDefaultTimeout(1);
       await page
@@ -246,7 +249,7 @@ describe('navigation', function () {
       const { page, server, puppeteer } = getTestState();
 
       // Hang for request to the empty.html
-      server.setRoute('/empty.html', (req, res) => {});
+      server.setRoute('/empty.html', () => {});
       let error = null;
       page.setDefaultTimeout(0);
       page.setDefaultNavigationTimeout(1);
@@ -389,7 +392,7 @@ describe('navigation', function () {
       const warningHandler = (w) => (warning = w);
       process.on('warning', warningHandler);
       for (let i = 0; i < 20; ++i)
-        await page.goto('asdf').catch((error) => {
+        await page.goto('asdf').catch(() => {
           /* swallow navigation error */
         });
       process.removeListener('warning', warningHandler);
@@ -601,7 +604,7 @@ describe('navigation', function () {
       async () => {
         const { page, server } = getTestState();
 
-        server.setRoute('/frames/style.css', (req, res) => {});
+        server.setRoute('/frames/style.css', () => {});
         const navigationPromise = page.goto(
           server.PREFIX + '/frames/one-frame.html'
         );
@@ -748,7 +751,7 @@ describe('navigation', function () {
         .catch((error_) => (error = error_));
       await Promise.all([
         server.waitForRequest('/empty.html'),
-        frame.evaluate(() => (window.location = '/empty.html')),
+        frame.evaluate(() => ((window as any).location = '/empty.html')),
       ]);
       await page.$eval('iframe', (frame) => frame.remove());
       await navigationPromise;
@@ -761,9 +764,9 @@ describe('navigation', function () {
       const { page, server } = getTestState();
 
       await page.goto(server.EMPTY_PAGE);
-      await page.evaluate(() => (window._foo = 10));
+      await page.evaluate(() => (globalThis._foo = 10));
       await page.reload();
-      expect(await page.evaluate(() => window._foo)).toBe(undefined);
+      expect(await page.evaluate(() => globalThis._foo)).toBe(undefined);
     });
   });
 });
diff --git a/test/network.spec.js b/test/network.spec.ts
similarity index 97%
rename from test/network.spec.js
rename to test/network.spec.ts
index 13f0efc3841e8..a80d347939e2d 100644
--- a/test/network.spec.js
+++ b/test/network.spec.ts
@@ -14,15 +14,17 @@
  * limitations under the License.
  */
 
-const fs = require('fs');
-const path = require('path');
-const utils = require('./utils');
-const expect = require('expect');
-const {
+import fs from 'fs';
+import path from 'path';
+import utils from './utils';
+import expect from 'expect';
+import {
   getTestState,
   setupTestBrowserHooks,
   setupTestPageAndContextHooks,
-} = require('./mocha-utils');
+  itFailsFirefox,
+  describeFailsFirefox,
+} from './mocha-utils';
 
 describe('network', function () {
   setupTestBrowserHooks();
@@ -184,7 +186,7 @@ describe('network', function () {
       await page.goto(server.PREFIX + '/serviceworkers/fetch/sw.html', {
         waitUntil: 'networkidle2',
       });
-      await page.evaluate(async () => await window.activationPromise);
+      await page.evaluate(async () => await globalThis.activationPromise);
       await page.reload();
 
       expect(responses.size).toBe(2);
@@ -409,9 +411,9 @@ describe('network', function () {
       const { page, server } = getTestState();
 
       const events = [];
-      page.on('request', (request) => events.push('request'));
-      page.on('response', (response) => events.push('response'));
-      page.on('requestfinished', (request) => events.push('requestfinished'));
+      page.on('request', () => events.push('request'));
+      page.on('response', () => events.push('response'));
+      page.on('requestfinished', () => events.push('requestfinished'));
       await page.goto(server.EMPTY_PAGE);
       expect(events).toEqual(['request', 'response', 'requestfinished']);
     });
@@ -514,6 +516,7 @@ describe('network', function () {
 
       let error = null;
       try {
+        // @ts-expect-error
         await page.setExtraHTTPHeaders({ foo: 1 });
       } catch (error_) {
         error = error_;
diff --git a/test/oopif.spec.js b/test/oopif.spec.ts
similarity index 95%
rename from test/oopif.spec.js
rename to test/oopif.spec.ts
index 97de9e5d8fb84..d58b8f568b652 100644
--- a/test/oopif.spec.js
+++ b/test/oopif.spec.ts
@@ -14,8 +14,8 @@
  * limitations under the License.
  */
 
-const expect = require('expect');
-const { getTestState } = require('./mocha-utils');
+import expect from 'expect';
+import { getTestState, describeChromeOnly } from './mocha-utils';
 
 describeChromeOnly('OOPIF', function () {
   /* We use a special browser for this test as we need the --site-per-process flag */
diff --git a/test/page.spec.js b/test/page.spec.ts
similarity index 92%
rename from test/page.spec.js
rename to test/page.spec.ts
index 8ee92899f8e2c..c258ea5d7bbcf 100644
--- a/test/page.spec.js
+++ b/test/page.spec.ts
@@ -13,17 +13,20 @@
  * See the License for the specific language governing permissions and
  * limitations under the License.
  */
-const fs = require('fs');
-const path = require('path');
-const utils = require('./utils');
+import fs from 'fs';
+import path from 'path';
+import utils from './utils';
 const { waitEvent } = utils;
-const expect = require('expect');
-const sinon = require('sinon');
-const {
+import expect from 'expect';
+import sinon from 'sinon';
+import {
   getTestState,
   setupTestBrowserHooks,
   setupTestPageAndContextHooks,
-} = require('./mocha-utils');
+  itFailsFirefox,
+  describeFailsFirefox,
+} from './mocha-utils';
+import { Page, Metrics } from '../src/common/Page';
 
 describe('Page', function () {
   setupTestBrowserHooks();
@@ -36,7 +39,7 @@ describe('Page', function () {
       let error = null;
       await Promise.all([
         newPage
-          .evaluate(() => new Promise((r) => {}))
+          .evaluate(() => new Promise(() => {}))
           .catch((error_) => (error = error_)),
         newPage.close(),
       ]);
@@ -160,7 +163,7 @@ describe('Page', function () {
 
       let error = null;
       page.on('error', (err) => (error = err));
-      page.goto('chrome://crash').catch((error_) => {});
+      page.goto('chrome://crash').catch(() => {});
       await waitEvent(page, 'error');
       expect(error.message).toBe('Page crashed!');
     });
@@ -171,7 +174,7 @@ describe('Page', function () {
       const { page } = getTestState();
 
       const [popup] = await Promise.all([
-        new Promise((x) => page.once('popup', x)),
+        new Promise<Page>((x) => page.once('popup', x)),
         page.evaluate(() => window.open('about:blank')),
       ]);
       expect(await page.evaluate(() => !!window.opener)).toBe(false);
@@ -181,7 +184,7 @@ describe('Page', function () {
       const { page } = getTestState();
 
       const [popup] = await Promise.all([
-        new Promise((x) => page.once('popup', x)),
+        new Promise<Page>((x) => page.once('popup', x)),
         page.evaluate(() => window.open('about:blank', null, 'noopener')),
       ]);
       expect(await page.evaluate(() => !!window.opener)).toBe(false);
@@ -193,7 +196,7 @@ describe('Page', function () {
       await page.goto(server.EMPTY_PAGE);
       await page.setContent('<a target=_blank href="/one-style.html">yo</a>');
       const [popup] = await Promise.all([
-        new Promise((x) => page.once('popup', x)),
+        new Promise<Page>((x) => page.once('popup', x)),
         page.click('a'),
       ]);
       expect(await page.evaluate(() => !!window.opener)).toBe(false);
@@ -207,7 +210,7 @@ describe('Page', function () {
         '<a target=_blank rel=noopener href="/one-style.html">yo</a>'
       );
       const [popup] = await Promise.all([
-        new Promise((x) => page.once('popup', x)),
+        new Promise<Page>((x) => page.once('popup', x)),
         page.$eval('a', (a) => a.click()),
       ]);
       expect(await page.evaluate(() => !!window.opener)).toBe(false);
@@ -221,7 +224,7 @@ describe('Page', function () {
         '<a target=_blank rel=noopener href="/one-style.html">yo</a>'
       );
       const [popup] = await Promise.all([
-        new Promise((x) => page.once('popup', x)),
+        new Promise<Page>((x) => page.once('popup', x)),
         page.click('a'),
       ]);
       expect(await page.evaluate(() => !!window.opener)).toBe(false);
@@ -257,6 +260,7 @@ describe('Page', function () {
       await page.goto(server.EMPTY_PAGE);
       let error = null;
       await context
+        // @ts-expect-error
         .overridePermissions(server.EMPTY_PAGE, ['foo'])
         .catch((error_) => (error = error_));
       expect(error.message).toBe('Unknown permission: foo');
@@ -282,30 +286,30 @@ describe('Page', function () {
 
       await page.goto(server.EMPTY_PAGE);
       await page.evaluate(() => {
-        window.events = [];
+        globalThis.events = [];
         return navigator.permissions
           .query({ name: 'geolocation' })
           .then(function (result) {
-            window.events.push(result.state);
+            globalThis.events.push(result.state);
             result.onchange = function () {
-              window.events.push(result.state);
+              globalThis.events.push(result.state);
             };
           });
       });
-      expect(await page.evaluate(() => window.events)).toEqual(['prompt']);
+      expect(await page.evaluate(() => globalThis.events)).toEqual(['prompt']);
       await context.overridePermissions(server.EMPTY_PAGE, []);
-      expect(await page.evaluate(() => window.events)).toEqual([
+      expect(await page.evaluate(() => globalThis.events)).toEqual([
         'prompt',
         'denied',
       ]);
       await context.overridePermissions(server.EMPTY_PAGE, ['geolocation']);
-      expect(await page.evaluate(() => window.events)).toEqual([
+      expect(await page.evaluate(() => globalThis.events)).toEqual([
         'prompt',
         'denied',
         'granted',
       ]);
       await context.clearPermissionOverrides();
-      expect(await page.evaluate(() => window.events)).toEqual([
+      expect(await page.evaluate(() => globalThis.events)).toEqual([
         'prompt',
         'denied',
         'granted',
@@ -404,7 +408,7 @@ describe('Page', function () {
       const { page } = getTestState();
 
       // Instantiate an object
-      await page.evaluate(() => (window.set = new Set(['hello', 'world'])));
+      await page.evaluate(() => (globalThis.set = new Set(['hello', 'world'])));
       const prototypeHandle = await page.evaluateHandle(() => Set.prototype);
       const objectsHandle = await page.queryObjects(prototypeHandle);
       const count = await page.evaluate(
@@ -423,7 +427,7 @@ describe('Page', function () {
 
       // Instantiate an object
       await page.goto(server.EMPTY_PAGE);
-      await page.evaluate(() => (window.set = new Set(['hello', 'world'])));
+      await page.evaluate(() => (globalThis.set = new Set(['hello', 'world'])));
       const prototypeHandle = await page.evaluateHandle(() => Set.prototype);
       const objectsHandle = await page.queryObjects(prototypeHandle);
       const count = await page.evaluate(
@@ -526,7 +530,7 @@ describe('Page', function () {
       const [message] = await Promise.all([
         waitEvent(page, 'console'),
         page.evaluate(
-          async (url) => fetch(url).catch((error) => {}),
+          async (url) => fetch(url).catch(() => {}),
           server.EMPTY_PAGE
         ),
       ]);
@@ -616,8 +620,8 @@ describe('Page', function () {
     it('metrics event fired on console.timeStamp', async () => {
       const { page } = getTestState();
 
-      const metricsPromise = new Promise((fulfill) =>
-        page.once('metrics', fulfill)
+      const metricsPromise = new Promise<{ metrics: Metrics; title: string }>(
+        (fulfill) => page.once('metrics', fulfill)
       );
       await page.evaluate(() => console.timeStamp('test42'));
       const metrics = await metricsPromise;
@@ -793,7 +797,7 @@ describe('Page', function () {
         return a * b;
       });
       const result = await page.evaluate(async function () {
-        return await compute(9, 4);
+        return await globalThis.compute(9, 4);
       });
       expect(result).toBe(36);
     });
@@ -805,7 +809,7 @@ describe('Page', function () {
       });
       const { message, stack } = await page.evaluate(async () => {
         try {
-          await woof();
+          await globalThis.woof();
         } catch (error) {
           return { message: error.message, stack: error.stack };
         }
@@ -821,7 +825,7 @@ describe('Page', function () {
       });
       const thrown = await page.evaluate(async () => {
         try {
-          await woof();
+          await globalThis.woof();
         } catch (error) {
           return error;
         }
@@ -835,7 +839,7 @@ describe('Page', function () {
       await page.exposeFunction('woof', function () {
         called = true;
       });
-      await page.evaluateOnNewDocument(() => woof());
+      await page.evaluateOnNewDocument(() => globalThis.woof());
       await page.reload();
       expect(called).toBe(true);
     });
@@ -848,7 +852,7 @@ describe('Page', function () {
 
       await page.goto(server.EMPTY_PAGE);
       const result = await page.evaluate(async function () {
-        return await compute(9, 4);
+        return await globalThis.compute(9, 4);
       });
       expect(result).toBe(36);
     });
@@ -860,7 +864,7 @@ describe('Page', function () {
       });
 
       const result = await page.evaluate(async function () {
-        return await compute(3, 5);
+        return await globalThis.compute(3, 5);
       });
       expect(result).toBe(15);
     });
@@ -874,7 +878,7 @@ describe('Page', function () {
       await page.goto(server.PREFIX + '/frames/nested-frames.html');
       const frame = page.frames()[1];
       const result = await frame.evaluate(async function () {
-        return await compute(3, 5);
+        return await globalThis.compute(3, 5);
       });
       expect(result).toBe(15);
     });
@@ -888,7 +892,7 @@ describe('Page', function () {
 
       const frame = page.frames()[1];
       const result = await frame.evaluate(async function () {
-        return await compute(3, 5);
+        return await globalThis.compute(3, 5);
       });
       expect(result).toBe(15);
     });
@@ -898,8 +902,8 @@ describe('Page', function () {
       await page.exposeFunction('complexObject', function (a, b) {
         return { x: a.x + b.x };
       });
-      const result = await page.evaluate(async () =>
-        complexObject({ x: 5 }, { x: 2 })
+      const result = await page.evaluate<{ x: number }>(async () =>
+        globalThis.complexObject({ x: 5 }, { x: 2 })
       );
       expect(result.x).toBe(7);
     });
@@ -993,7 +997,7 @@ describe('Page', function () {
 
       const imgPath = '/img.png';
       // stall for image
-      server.setRoute(imgPath, (req, res) => {});
+      server.setRoute(imgPath, () => {});
       let error = null;
       await page
         .setContent(`<img src="${server.PREFIX + imgPath}"></img>`, {
@@ -1008,7 +1012,7 @@ describe('Page', function () {
       page.setDefaultNavigationTimeout(1);
       const imgPath = '/img.png';
       // stall for image
-      server.setRoute(imgPath, (req, res) => {});
+      server.setRoute(imgPath, () => {});
       let error = null;
       await page
         .setContent(`<img src="${server.PREFIX + imgPath}"></img>`)
@@ -1074,13 +1078,13 @@ describe('Page', function () {
       await page
         .addScriptTag({ content: 'window.__injected = 42;' })
         .catch((error) => void error);
-      expect(await page.evaluate(() => window.__injected)).toBe(undefined);
+      expect(await page.evaluate(() => globalThis.__injected)).toBe(undefined);
 
       // By-pass CSP and try one more time.
       await page.setBypassCSP(true);
       await page.reload();
       await page.addScriptTag({ content: 'window.__injected = 42;' });
-      expect(await page.evaluate(() => window.__injected)).toBe(42);
+      expect(await page.evaluate(() => globalThis.__injected)).toBe(42);
     });
 
     it('should bypass CSP header', async () => {
@@ -1092,13 +1096,13 @@ describe('Page', function () {
       await page
         .addScriptTag({ content: 'window.__injected = 42;' })
         .catch((error) => void error);
-      expect(await page.evaluate(() => window.__injected)).toBe(undefined);
+      expect(await page.evaluate(() => globalThis.__injected)).toBe(undefined);
 
       // By-pass CSP and try one more time.
       await page.setBypassCSP(true);
       await page.reload();
       await page.addScriptTag({ content: 'window.__injected = 42;' });
-      expect(await page.evaluate(() => window.__injected)).toBe(42);
+      expect(await page.evaluate(() => globalThis.__injected)).toBe(42);
     });
 
     it('should bypass after cross-process navigation', async () => {
@@ -1107,11 +1111,11 @@ describe('Page', function () {
       await page.setBypassCSP(true);
       await page.goto(server.PREFIX + '/csp.html');
       await page.addScriptTag({ content: 'window.__injected = 42;' });
-      expect(await page.evaluate(() => window.__injected)).toBe(42);
+      expect(await page.evaluate(() => globalThis.__injected)).toBe(42);
 
       await page.goto(server.CROSS_PROCESS_PREFIX + '/csp.html');
       await page.addScriptTag({ content: 'window.__injected = 42;' });
-      expect(await page.evaluate(() => window.__injected)).toBe(42);
+      expect(await page.evaluate(() => globalThis.__injected)).toBe(42);
     });
     it('should bypass CSP in iframes as well', async () => {
       const { page, server } = getTestState();
@@ -1127,7 +1131,9 @@ describe('Page', function () {
         await frame
           .addScriptTag({ content: 'window.__injected = 42;' })
           .catch((error) => void error);
-        expect(await frame.evaluate(() => window.__injected)).toBe(undefined);
+        expect(await frame.evaluate(() => globalThis.__injected)).toBe(
+          undefined
+        );
       }
 
       // By-pass CSP and try one more time.
@@ -1143,7 +1149,7 @@ describe('Page', function () {
         await frame
           .addScriptTag({ content: 'window.__injected = 42;' })
           .catch((error) => void error);
-        expect(await frame.evaluate(() => window.__injected)).toBe(42);
+        expect(await frame.evaluate(() => globalThis.__injected)).toBe(42);
       }
     });
   });
@@ -1154,6 +1160,7 @@ describe('Page', function () {
 
       let error = null;
       try {
+        // @ts-expect-error
         await page.addScriptTag('/injectedfile.js');
       } catch (error_) {
         error = error_;
@@ -1169,7 +1176,7 @@ describe('Page', function () {
       await page.goto(server.EMPTY_PAGE);
       const scriptHandle = await page.addScriptTag({ url: '/injectedfile.js' });
       expect(scriptHandle.asElement()).not.toBeNull();
-      expect(await page.evaluate(() => __injected)).toBe(42);
+      expect(await page.evaluate(() => globalThis.__injected)).toBe(42);
     });
 
     it('should work with a url and type=module', async () => {
@@ -1177,7 +1184,7 @@ describe('Page', function () {
 
       await page.goto(server.EMPTY_PAGE);
       await page.addScriptTag({ url: '/es6/es6import.js', type: 'module' });
-      expect(await page.evaluate(() => __es6injected)).toBe(42);
+      expect(await page.evaluate(() => globalThis.__es6injected)).toBe(42);
     });
 
     it('should work with a path and type=module', async () => {
@@ -1189,7 +1196,7 @@ describe('Page', function () {
         type: 'module',
       });
       await page.waitForFunction('window.__es6injected');
-      expect(await page.evaluate(() => __es6injected)).toBe(42);
+      expect(await page.evaluate(() => globalThis.__es6injected)).toBe(42);
     });
 
     it('should work with a content and type=module', async () => {
@@ -1201,7 +1208,7 @@ describe('Page', function () {
         type: 'module',
       });
       await page.waitForFunction('window.__es6injected');
-      expect(await page.evaluate(() => __es6injected)).toBe(42);
+      expect(await page.evaluate(() => globalThis.__es6injected)).toBe(42);
     });
 
     it('should throw an error if loading from url fail', async () => {
@@ -1225,7 +1232,7 @@ describe('Page', function () {
         path: path.join(__dirname, 'assets/injectedfile.js'),
       });
       expect(scriptHandle.asElement()).not.toBeNull();
-      expect(await page.evaluate(() => __injected)).toBe(42);
+      expect(await page.evaluate(() => globalThis.__injected)).toBe(42);
     });
 
     it('should include sourcemap when path is provided', async () => {
@@ -1235,7 +1242,9 @@ describe('Page', function () {
       await page.addScriptTag({
         path: path.join(__dirname, 'assets/injectedfile.js'),
       });
-      const result = await page.evaluate(() => __injectedError.stack);
+      const result = await page.evaluate(
+        () => globalThis.__injectedError.stack
+      );
       expect(result).toContain(path.join('assets', 'injectedfile.js'));
     });
 
@@ -1247,7 +1256,7 @@ describe('Page', function () {
         content: 'window.__injected = 35;',
       });
       expect(scriptHandle.asElement()).not.toBeNull();
-      expect(await page.evaluate(() => __injected)).toBe(35);
+      expect(await page.evaluate(() => globalThis.__injected)).toBe(35);
     });
 
     // @see https://github.com/puppeteer/puppeteer/issues/4840
@@ -1280,6 +1289,7 @@ describe('Page', function () {
 
       let error = null;
       try {
+        // @ts-expect-error
         await page.addStyleTag('/injectedstyle.css');
       } catch (error_) {
         error = error_;
@@ -1485,16 +1495,24 @@ describe('Page', function () {
 
       await page.goto(server.PREFIX + '/input/select.html');
       await page.select('select', 'blue');
-      expect(await page.evaluate(() => result.onInput)).toEqual(['blue']);
-      expect(await page.evaluate(() => result.onChange)).toEqual(['blue']);
+      expect(await page.evaluate(() => globalThis.result.onInput)).toEqual([
+        'blue',
+      ]);
+      expect(await page.evaluate(() => globalThis.result.onChange)).toEqual([
+        'blue',
+      ]);
     });
     it('should select only first option', async () => {
       const { page, server } = getTestState();
 
       await page.goto(server.PREFIX + '/input/select.html');
       await page.select('select', 'blue', 'green', 'red');
-      expect(await page.evaluate(() => result.onInput)).toEqual(['blue']);
-      expect(await page.evaluate(() => result.onChange)).toEqual(['blue']);
+      expect(await page.evaluate(() => globalThis.result.onInput)).toEqual([
+        'blue',
+      ]);
+      expect(await page.evaluate(() => globalThis.result.onChange)).toEqual([
+        'blue',
+      ]);
     });
     it('should not throw when select causes navigation', async () => {
       const { page, server } = getTestState();
@@ -1503,7 +1521,7 @@ describe('Page', function () {
       await page.$eval('select', (select) =>
         select.addEventListener(
           'input',
-          () => (window.location = '/empty.html')
+          () => ((window as any).location = '/empty.html')
         )
       );
       await Promise.all([
@@ -1516,14 +1534,14 @@ describe('Page', function () {
       const { page, server } = getTestState();
 
       await page.goto(server.PREFIX + '/input/select.html');
-      await page.evaluate(() => makeMultiple());
+      await page.evaluate(() => globalThis.makeMultiple());
       await page.select('select', 'blue', 'green', 'red');
-      expect(await page.evaluate(() => result.onInput)).toEqual([
+      expect(await page.evaluate(() => globalThis.result.onInput)).toEqual([
         'blue',
         'green',
         'red',
       ]);
-      expect(await page.evaluate(() => result.onChange)).toEqual([
+      expect(await page.evaluate(() => globalThis.result.onChange)).toEqual([
         'blue',
         'green',
         'red',
@@ -1534,12 +1552,12 @@ describe('Page', function () {
 
       await page.goto(server.PREFIX + '/input/select.html');
       await page.select('select', 'blue');
-      expect(await page.evaluate(() => result.onBubblingInput)).toEqual([
-        'blue',
-      ]);
-      expect(await page.evaluate(() => result.onBubblingChange)).toEqual([
-        'blue',
-      ]);
+      expect(
+        await page.evaluate(() => globalThis.result.onBubblingInput)
+      ).toEqual(['blue']);
+      expect(
+        await page.evaluate(() => globalThis.result.onBubblingChange)
+      ).toEqual(['blue']);
     });
     it('should throw when element is not a <select>', async () => {
       const { page, server } = getTestState();
@@ -1560,7 +1578,7 @@ describe('Page', function () {
       const { page, server } = getTestState();
 
       await page.goto(server.PREFIX + '/input/select.html');
-      await page.evaluate(() => makeMultiple());
+      await page.evaluate(() => globalThis.makeMultiple());
       const result = await page.select('select', 'blue', 'black', 'magenta');
       expect(
         result.reduce(
@@ -1594,12 +1612,14 @@ describe('Page', function () {
       const { page, server } = getTestState();
 
       await page.goto(server.PREFIX + '/input/select.html');
-      await page.evaluate(() => makeMultiple());
+      await page.evaluate(() => globalThis.makeMultiple());
       await page.select('select', 'blue', 'black', 'magenta');
       await page.select('select');
       expect(
         await page.$eval('select', (select) =>
-          Array.from(select.options).every((option) => !option.selected)
+          Array.from(select.options).every(
+            (option: HTMLOptionElement) => !option.selected
+          )
         )
       ).toEqual(true);
     });
@@ -1611,7 +1631,9 @@ describe('Page', function () {
       await page.select('select');
       expect(
         await page.$eval('select', (select) =>
-          Array.from(select.options).every((option) => !option.selected)
+          Array.from(select.options).every(
+            (option: HTMLOptionElement) => !option.selected
+          )
         )
       ).toEqual(true);
     });
@@ -1621,6 +1643,7 @@ describe('Page', function () {
       await page.setContent('<select><option value="12"/></select>');
       let error = null;
       try {
+        // @ts-expect-error
         await page.select('select', 12);
       } catch (error_) {
         error = error_;
@@ -1636,8 +1659,12 @@ describe('Page', function () {
         await page.goto(server.PREFIX + '/input/select.html');
         await page.evaluate(() => (window.Event = null));
         await page.select('select', 'blue');
-        expect(await page.evaluate(() => result.onInput)).toEqual(['blue']);
-        expect(await page.evaluate(() => result.onChange)).toEqual(['blue']);
+        expect(await page.evaluate(() => globalThis.result.onInput)).toEqual([
+          'blue',
+        ]);
+        expect(await page.evaluate(() => globalThis.result.onChange)).toEqual([
+          'blue',
+        ]);
       }
     );
   });
@@ -1646,7 +1673,7 @@ describe('Page', function () {
     itFailsFirefox('should work with window.close', async () => {
       const { page, context } = getTestState();
 
-      const newPagePromise = new Promise((fulfill) =>
+      const newPagePromise = new Promise<Page>((fulfill) =>
         context.once('targetcreated', (target) => fulfill(target.page()))
       );
       await page.evaluate(
diff --git a/test/queryselector.spec.js b/test/queryselector.spec.ts
similarity index 99%
rename from test/queryselector.spec.js
rename to test/queryselector.spec.ts
index 720095e674fb6..5dbf06f8952fc 100644
--- a/test/queryselector.spec.js
+++ b/test/queryselector.spec.ts
@@ -13,12 +13,12 @@
  * See the License for the specific language governing permissions and
  * limitations under the License.
  */
-const expect = require('expect');
-const {
+import expect from 'expect';
+import {
   getTestState,
   setupTestBrowserHooks,
   setupTestPageAndContextHooks,
-} = require('./mocha-utils');
+} from './mocha-utils';
 
 describe('querySelector', function () {
   setupTestBrowserHooks();
diff --git a/test/requestinterception.spec.js b/test/requestinterception.spec.ts
similarity index 98%
rename from test/requestinterception.spec.js
rename to test/requestinterception.spec.ts
index 8c65771dc804a..005448818cbf2 100644
--- a/test/requestinterception.spec.js
+++ b/test/requestinterception.spec.ts
@@ -14,15 +14,16 @@
  * limitations under the License.
  */
 
-const fs = require('fs');
-const path = require('path');
-const utils = require('./utils');
-const expect = require('expect');
-const {
+import fs from 'fs';
+import path from 'path';
+import utils from './utils';
+import expect from 'expect';
+import {
   getTestState,
   setupTestBrowserHooks,
   setupTestPageAndContextHooks,
-} = require('./mocha-utils');
+  describeFailsFirefox,
+} from './mocha-utils';
 
 describe('request interception', function () {
   setupTestBrowserHooks();
@@ -188,7 +189,7 @@ describe('request interception', function () {
         else request.continue();
       });
       let failedRequests = 0;
-      page.on('requestfailed', (event) => ++failedRequests);
+      page.on('requestfailed', () => ++failedRequests);
       const response = await page.goto(server.PREFIX + '/one-style.html');
       expect(response.ok()).toBe(true);
       expect(response.request().failure()).toBe(null);
@@ -203,7 +204,7 @@ describe('request interception', function () {
       });
       let failedRequest = null;
       page.on('requestfailed', (request) => (failedRequest = request));
-      await page.goto(server.EMPTY_PAGE).catch((error) => {});
+      await page.goto(server.EMPTY_PAGE).catch(() => {});
       expect(failedRequest).toBeTruthy();
       expect(failedRequest.failure().errorText).toBe(
         'net::ERR_INTERNET_DISCONNECTED'
@@ -345,13 +346,13 @@ describe('request interception', function () {
         Promise.all([
           fetch('/zzz')
             .then((response) => response.text())
-            .catch((error) => 'FAILED'),
+            .catch(() => 'FAILED'),
           fetch('/zzz')
             .then((response) => response.text())
-            .catch((error) => 'FAILED'),
+            .catch(() => 'FAILED'),
           fetch('/zzz')
             .then((response) => response.text())
-            .catch((error) => 'FAILED'),
+            .catch(() => 'FAILED'),
         ])
       );
       expect(results).toEqual(['11', 'FAILED', '22']);
@@ -665,6 +666,8 @@ describe('request interception', function () {
         return new Promise((fulfill) => (img.onload = fulfill));
       }, server.PREFIX);
       const img = await page.$('img');
+      // TODO (@jackfranklin): toBeGolden type fix
+      // @ts-expect-error
       expect(await img.screenshot()).toBeGolden('mock-binary-response.png');
     });
     it('should stringify intercepted request response headers', async () => {
diff --git a/test/screenshot.spec.js b/test/screenshot.spec.ts
similarity index 88%
rename from test/screenshot.spec.js
rename to test/screenshot.spec.ts
index cb756127c378d..1288924fa100d 100644
--- a/test/screenshot.spec.js
+++ b/test/screenshot.spec.ts
@@ -14,12 +14,13 @@
  * limitations under the License.
  */
 
-const expect = require('expect');
-const {
+import expect from 'expect';
+import {
   getTestState,
   setupTestBrowserHooks,
   setupTestPageAndContextHooks,
-} = require('./mocha-utils');
+  itFailsFirefox,
+} from './mocha-utils';
 
 describe('Screenshots', function () {
   setupTestBrowserHooks();
@@ -32,6 +33,8 @@ describe('Screenshots', function () {
       await page.setViewport({ width: 500, height: 500 });
       await page.goto(server.PREFIX + '/grid.html');
       const screenshot = await page.screenshot();
+      // TODO (@jackfranklin): toBeGolden type fix
+      // @ts-expect-error
       expect(screenshot).toBeGolden('screenshot-sanity.png');
     });
     itFailsFirefox('should clip rect', async () => {
@@ -47,6 +50,8 @@ describe('Screenshots', function () {
           height: 100,
         },
       });
+      // TODO (@jackfranklin): toBeGolden type fix
+      // @ts-expect-error
       expect(screenshot).toBeGolden('screenshot-clip-rect.png');
     });
     itFailsFirefox('should clip elements to the viewport', async () => {
@@ -62,6 +67,8 @@ describe('Screenshots', function () {
           height: 100,
         },
       });
+      // TODO (@jackfranklin): toBeGolden type fix
+      // @ts-expect-error
       expect(screenshot).toBeGolden('screenshot-offscreen-clip.png');
     });
     it('should run in parallel', async () => {
@@ -83,6 +90,8 @@ describe('Screenshots', function () {
         );
       }
       const screenshots = await Promise.all(promises);
+      // TODO (@jackfranklin): toBeGolden type fix
+      // @ts-expect-error
       expect(screenshots[1]).toBeGolden('grid-cell-1.png');
     });
     itFailsFirefox('should take fullPage screenshots', async () => {
@@ -93,6 +102,8 @@ describe('Screenshots', function () {
       const screenshot = await page.screenshot({
         fullPage: true,
       });
+      // TODO (@jackfranklin): toBeGolden type fix
+      // @ts-expect-error
       expect(screenshot).toBeGolden('screenshot-grid-fullpage.png');
     });
     it('should run in parallel in multiple pages', async () => {
@@ -117,6 +128,8 @@ describe('Screenshots', function () {
         );
       const screenshots = await Promise.all(promises);
       for (let i = 0; i < N; ++i)
+        // TODO (@jackfranklin): toBeGolden type fix
+        // @ts-expect-error
         expect(screenshots[i]).toBeGolden(`grid-cell-${i}.png`);
       await Promise.all(pages.map((page) => page.close()));
     });
@@ -126,6 +139,8 @@ describe('Screenshots', function () {
       await page.setViewport({ width: 100, height: 100 });
       await page.goto(server.EMPTY_PAGE);
       const screenshot = await page.screenshot({ omitBackground: true });
+      // TODO (@jackfranklin): toBeGolden type fix
+      // @ts-expect-error
       expect(screenshot).toBeGolden('transparent.png');
     });
     itFailsFirefox('should render white background on jpeg file', async () => {
@@ -137,6 +152,8 @@ describe('Screenshots', function () {
         omitBackground: true,
         type: 'jpeg',
       });
+      // TODO (@jackfranklin): toBeGolden type fix
+      // @ts-expect-error
       expect(screenshot).toBeGolden('white.jpg');
     });
     it('should work with odd clip size on Retina displays', async () => {
@@ -150,6 +167,8 @@ describe('Screenshots', function () {
           height: 11,
         },
       });
+      // TODO (@jackfranklin): toBeGolden type fix
+      // @ts-expect-error
       expect(screenshot).toBeGolden('screenshot-clip-odd-size.png');
     });
     itFailsFirefox('should return base64', async () => {
@@ -160,6 +179,8 @@ describe('Screenshots', function () {
       const screenshot = await page.screenshot({
         encoding: 'base64',
       });
+      // TODO (@jackfranklin): toBeGolden type fix
+      // @ts-expect-error
       expect(Buffer.from(screenshot, 'base64')).toBeGolden(
         'screenshot-sanity.png'
       );
@@ -175,6 +196,8 @@ describe('Screenshots', function () {
       await page.evaluate(() => window.scrollBy(50, 100));
       const elementHandle = await page.$('.box:nth-of-type(3)');
       const screenshot = await elementHandle.screenshot();
+      // TODO (@jackfranklin): toBeGolden type fix
+      // @ts-expect-error
       expect(screenshot).toBeGolden('screenshot-element-bounding-box.png');
     });
     it('should take into account padding and border', async () => {
@@ -194,6 +217,8 @@ describe('Screenshots', function () {
       `);
       const elementHandle = await page.$('div');
       const screenshot = await elementHandle.screenshot();
+      // TODO (@jackfranklin): toBeGolden type fix
+      // @ts-expect-error
       expect(screenshot).toBeGolden('screenshot-element-padding-border.png');
     });
     it('should capture full element when larger than viewport', async () => {
@@ -218,6 +243,8 @@ describe('Screenshots', function () {
       `);
       const elementHandle = await page.$('div.to-screenshot');
       const screenshot = await elementHandle.screenshot();
+      // TODO (@jackfranklin): toBeGolden type fix
+      // @ts-expect-error
       expect(screenshot).toBeGolden(
         'screenshot-element-larger-than-viewport.png'
       );
@@ -252,6 +279,8 @@ describe('Screenshots', function () {
       `);
       const elementHandle = await page.$('div.to-screenshot');
       const screenshot = await elementHandle.screenshot();
+      // TODO (@jackfranklin): toBeGolden type fix
+      // @ts-expect-error
       expect(screenshot).toBeGolden(
         'screenshot-element-scrolled-into-view.png'
       );
@@ -269,6 +298,8 @@ describe('Screenshots', function () {
                                         transform: rotateZ(200deg);">&nbsp;</div>`);
       const elementHandle = await page.$('div');
       const screenshot = await elementHandle.screenshot();
+      // TODO (@jackfranklin): toBeGolden type fix
+      // @ts-expect-error
       expect(screenshot).toBeGolden('screenshot-element-rotate.png');
     });
     itFailsFirefox('should fail to screenshot a detached element', async () => {
@@ -300,6 +331,8 @@ describe('Screenshots', function () {
       );
       const elementHandle = await page.$('div');
       const screenshot = await elementHandle.screenshot();
+      // TODO (@jackfranklin): toBeGolden type fix
+      // @ts-expect-error
       expect(screenshot).toBeGolden('screenshot-element-fractional.png');
     });
     itFailsFirefox('should work for an element with an offset', async () => {
@@ -310,6 +343,8 @@ describe('Screenshots', function () {
       );
       const elementHandle = await page.$('div');
       const screenshot = await elementHandle.screenshot();
+      // TODO (@jackfranklin): toBeGolden type fix
+      // @ts-expect-error
       expect(screenshot).toBeGolden('screenshot-element-fractional-offset.png');
     });
   });
diff --git a/test/target.spec.js b/test/target.spec.ts
similarity index 94%
rename from test/target.spec.js
rename to test/target.spec.ts
index 288daae3873f6..54e0fa2854b76 100644
--- a/test/target.spec.js
+++ b/test/target.spec.ts
@@ -14,14 +14,16 @@
  * limitations under the License.
  */
 
-const utils = require('./utils');
+import utils from './utils';
 const { waitEvent } = utils;
-const expect = require('expect');
-const {
+import expect from 'expect';
+import {
   getTestState,
   setupTestBrowserHooks,
   setupTestPageAndContextHooks,
-} = require('./mocha-utils');
+  itFailsFirefox,
+} from './mocha-utils';
+import { Target } from '../src/common/Target';
 
 describe('Target', function () {
   setupTestBrowserHooks();
@@ -112,7 +114,7 @@ describe('Target', function () {
       const { page, server, context } = getTestState();
 
       await page.goto(server.EMPTY_PAGE);
-      const createdTarget = new Promise((fulfill) =>
+      const createdTarget = new Promise<Target>((fulfill) =>
         context.once('targetcreated', (target) => fulfill(target))
       );
 
@@ -127,7 +129,7 @@ describe('Target', function () {
         context.once('targetdestroyed', (target) => fulfill(target))
       );
       await page.evaluate(() =>
-        window.registrationPromise.then((registration) =>
+        globalThis.registrationPromise.then((registration) =>
           registration.unregister()
         )
       );
@@ -166,7 +168,7 @@ describe('Target', function () {
     const { page, server, context } = getTestState();
 
     await page.goto(server.EMPTY_PAGE);
-    let changedTarget = new Promise((fulfill) =>
+    let changedTarget = new Promise<Target>((fulfill) =>
       context.once('targetchanged', (target) => fulfill(target))
     );
     await page.goto(server.CROSS_PROCESS_PREFIX + '/');
@@ -184,7 +186,7 @@ describe('Target', function () {
     let targetChanged = false;
     const listener = () => (targetChanged = true);
     context.on('targetchanged', listener);
-    const targetPromise = new Promise((fulfill) =>
+    const targetPromise = new Promise<Target>((fulfill) =>
       context.once('targetcreated', (target) => fulfill(target))
     );
     const newPagePromise = context.newPage();
@@ -192,7 +194,7 @@ describe('Target', function () {
     expect(target.url()).toBe('about:blank');
 
     const newPage = await newPagePromise;
-    const targetPromise2 = new Promise((fulfill) =>
+    const targetPromise2 = new Promise<Target>((fulfill) =>
       context.once('targetcreated', (target) => fulfill(target))
     );
     const evaluatePromise = newPage.evaluate(() => window.open('about:blank'));
@@ -200,10 +202,7 @@ describe('Target', function () {
     expect(target2.url()).toBe('about:blank');
     await evaluatePromise;
     await newPage.close();
-    expect(targetChanged).toBe(
-      false,
-      'target should not be reported as changed'
-    );
+    expect(targetChanged).toBe(false);
     context.removeListener('targetchanged', listener);
   });
   itFailsFirefox(
@@ -240,7 +239,7 @@ describe('Target', function () {
 
     await page.goto(server.EMPTY_PAGE);
     const [createdTarget] = await Promise.all([
-      new Promise((fulfill) =>
+      new Promise<Target>((fulfill) =>
         context.once('targetcreated', (target) => fulfill(target))
       ),
       page.goto(server.PREFIX + '/popup/window-open.html'),
diff --git a/test/touchscreen.spec.js b/test/touchscreen.spec.ts
similarity index 86%
rename from test/touchscreen.spec.js
rename to test/touchscreen.spec.ts
index a25cff2b63bf4..8f4129a3edaa0 100644
--- a/test/touchscreen.spec.js
+++ b/test/touchscreen.spec.ts
@@ -14,12 +14,13 @@
  * limitations under the License.
  */
 
-const expect = require('expect');
-const {
+import expect from 'expect';
+import {
   getTestState,
   setupTestBrowserHooks,
   setupTestPageAndContextHooks,
-} = require('./mocha-utils');
+  describeFailsFirefox,
+} from './mocha-utils';
 
 describeFailsFirefox('Touchscreen', function () {
   setupTestBrowserHooks();
@@ -31,7 +32,7 @@ describeFailsFirefox('Touchscreen', function () {
     await page.emulate(iPhone);
     await page.goto(server.PREFIX + '/input/button.html');
     await page.tap('button');
-    expect(await page.evaluate(() => result)).toBe('Clicked');
+    expect(await page.evaluate(() => globalThis.result)).toBe('Clicked');
   });
   it('should report touches', async () => {
     const { puppeteer, page, server } = getTestState();
@@ -40,7 +41,7 @@ describeFailsFirefox('Touchscreen', function () {
     await page.goto(server.PREFIX + '/input/touches.html');
     const button = await page.$('button');
     await button.tap();
-    expect(await page.evaluate(() => getResult())).toEqual([
+    expect(await page.evaluate(() => globalThis.getResult())).toEqual([
       'Touchstart: 0',
       'Touchend: 0',
     ]);
diff --git a/test/tracing.spec.js b/test/tracing.spec.ts
similarity index 93%
rename from test/tracing.spec.js
rename to test/tracing.spec.ts
index e0f15e4a62f78..7b5afeac9d9b4 100644
--- a/test/tracing.spec.js
+++ b/test/tracing.spec.ts
@@ -14,10 +14,10 @@
  * limitations under the License.
  */
 
-const fs = require('fs');
-const path = require('path');
-const expect = require('expect');
-const { getTestState } = require('./mocha-utils');
+import fs from 'fs';
+import path from 'path';
+import expect from 'expect';
+import { getTestState, describeChromeOnly } from './mocha-utils';
 
 describeChromeOnly('Tracing', function () {
   let outputFile;
@@ -60,7 +60,9 @@ describeChromeOnly('Tracing', function () {
     });
     await page.tracing.stop();
 
-    const traceJson = JSON.parse(fs.readFileSync(outputFile));
+    const traceJson = JSON.parse(
+      fs.readFileSync(outputFile, { encoding: 'utf8' })
+    );
     expect(traceJson.metadata['trace-config']).toContain(
       'disabled-by-default-v8.cpu_profiler.hires'
     );
@@ -100,7 +102,7 @@ describeChromeOnly('Tracing', function () {
     await page.tracing.start({ screenshots: true });
     await page.goto(server.PREFIX + '/grid.html');
     const oldBufferConcat = Buffer.concat;
-    Buffer.concat = (bufs) => {
+    Buffer.concat = () => {
       throw 'error';
     };
     const trace = await page.tracing.stop();
diff --git a/test/tsconfig.json b/test/tsconfig.json
new file mode 100644
index 0000000000000..8b1f1e866cbd4
--- /dev/null
+++ b/test/tsconfig.json
@@ -0,0 +1,7 @@
+{
+  "extends": "../tsconfig.json",
+  "compilerOptions": {
+    "noEmit": true
+  },
+  "include": ["*.ts", "*.js"]
+}
diff --git a/test/utils.js b/test/utils.js
index 0b3f2bfd25da3..935b44d98efda 100644
--- a/test/utils.js
+++ b/test/utils.js
@@ -14,6 +14,9 @@
  * limitations under the License.
  */
 
+// TODO (@jackfranklin): convert to TS and enable type checking.
+
+// @ts-nocheck
 const fs = require('fs');
 const path = require('path');
 const expect = require('expect');
diff --git a/test/waittask.spec.js b/test/waittask.spec.ts
similarity index 92%
rename from test/waittask.spec.js
rename to test/waittask.spec.ts
index efb5f6ef8bfd1..9c216c1068552 100644
--- a/test/waittask.spec.js
+++ b/test/waittask.spec.ts
@@ -14,13 +14,14 @@
  * limitations under the License.
  */
 
-const utils = require('./utils');
-const expect = require('expect');
-const {
+import utils from './utils';
+import expect from 'expect';
+import {
   getTestState,
   setupTestBrowserHooks,
   setupTestPageAndContextHooks,
-} = require('./mocha-utils');
+  itFailsFirefox,
+} from './mocha-utils';
 
 describe('waittask specs', function () {
   setupTestBrowserHooks();
@@ -86,6 +87,7 @@ describe('waittask specs', function () {
       const { page } = getTestState();
 
       let error = null;
+      // @ts-expect-error
       await page.waitFor({ foo: 'bar' }).catch((error_) => (error = error_));
       expect(error.message).toContain('Unsupported target type');
     });
@@ -101,7 +103,7 @@ describe('waittask specs', function () {
       const { page } = getTestState();
 
       const watchdog = page.waitForFunction('window.__FOO === 1');
-      await page.evaluate(() => (window.__FOO = 1));
+      await page.evaluate(() => (globalThis.__FOO = 1));
       await watchdog;
     });
     itFailsFirefox(
@@ -109,9 +111,9 @@ describe('waittask specs', function () {
       async () => {
         const { page } = getTestState();
 
-        await page.evaluateOnNewDocument(() => (window.__RELOADED = true));
+        await page.evaluateOnNewDocument(() => (globalThis.__RELOADED = true));
         await page.waitForFunction(() => {
-          if (!window.__RELOADED) window.location.reload();
+          if (!globalThis.__RELOADED) window.location.reload();
           return true;
         });
       }
@@ -123,9 +125,9 @@ describe('waittask specs', function () {
       const startTime = Date.now();
       const polling = 100;
       const watchdog = page
-        .waitForFunction(() => window.__FOO === 'hit', { polling })
+        .waitForFunction(() => globalThis.__FOO === 'hit', { polling })
         .then(() => (success = true));
-      await page.evaluate(() => (window.__FOO = 'hit'));
+      await page.evaluate(() => (globalThis.__FOO = 'hit'));
       expect(success).toBe(false);
       await page.evaluate(() =>
         document.body.appendChild(document.createElement('div'))
@@ -139,9 +141,9 @@ describe('waittask specs', function () {
       const startTime = Date.now();
       const polling = 100;
       const watchdog = page
-        .waitForFunction(async () => window.__FOO === 'hit', { polling })
+        .waitForFunction(async () => globalThis.__FOO === 'hit', { polling })
         .then(() => (success = true));
-      await page.evaluate(async () => (window.__FOO = 'hit'));
+      await page.evaluate(async () => (globalThis.__FOO = 'hit'));
       expect(success).toBe(false);
       await page.evaluate(async () =>
         document.body.appendChild(document.createElement('div'))
@@ -154,9 +156,11 @@ describe('waittask specs', function () {
 
       let success = false;
       const watchdog = page
-        .waitForFunction(() => window.__FOO === 'hit', { polling: 'mutation' })
+        .waitForFunction(() => globalThis.__FOO === 'hit', {
+          polling: 'mutation',
+        })
         .then(() => (success = true));
-      await page.evaluate(() => (window.__FOO = 'hit'));
+      await page.evaluate(() => (globalThis.__FOO = 'hit'));
       expect(success).toBe(false);
       await page.evaluate(() =>
         document.body.appendChild(document.createElement('div'))
@@ -168,11 +172,11 @@ describe('waittask specs', function () {
 
       let success = false;
       const watchdog = page
-        .waitForFunction(async () => window.__FOO === 'hit', {
+        .waitForFunction(async () => globalThis.__FOO === 'hit', {
           polling: 'mutation',
         })
         .then(() => (success = true));
-      await page.evaluate(async () => (window.__FOO = 'hit'));
+      await page.evaluate(async () => (globalThis.__FOO = 'hit'));
       expect(success).toBe(false);
       await page.evaluate(async () =>
         document.body.appendChild(document.createElement('div'))
@@ -182,22 +186,22 @@ describe('waittask specs', function () {
     it('should poll on raf', async () => {
       const { page } = getTestState();
 
-      const watchdog = page.waitForFunction(() => window.__FOO === 'hit', {
+      const watchdog = page.waitForFunction(() => globalThis.__FOO === 'hit', {
         polling: 'raf',
       });
-      await page.evaluate(() => (window.__FOO = 'hit'));
+      await page.evaluate(() => (globalThis.__FOO = 'hit'));
       await watchdog;
     });
     it('should poll on raf async', async () => {
       const { page } = getTestState();
 
       const watchdog = page.waitForFunction(
-        async () => window.__FOO === 'hit',
+        async () => globalThis.__FOO === 'hit',
         {
           polling: 'raf',
         }
       );
-      await page.evaluate(async () => (window.__FOO = 'hit'));
+      await page.evaluate(async () => (globalThis.__FOO = 'hit'));
       await watchdog;
     });
     itFailsFirefox('should work with strict CSP policy', async () => {
@@ -208,9 +212,9 @@ describe('waittask specs', function () {
       let error = null;
       await Promise.all([
         page
-          .waitForFunction(() => window.__FOO === 'hit', { polling: 'raf' })
+          .waitForFunction(() => globalThis.__FOO === 'hit', { polling: 'raf' })
           .catch((error_) => (error = error_)),
-        page.evaluate(() => (window.__FOO = 'hit')),
+        page.evaluate(() => (globalThis.__FOO = 'hit')),
       ]);
       expect(error).toBe(null);
     });
@@ -288,13 +292,13 @@ describe('waittask specs', function () {
 
       const watchdog = page.waitForFunction(
         () => {
-          window.__counter = (window.__counter || 0) + 1;
-          return window.__injected;
+          globalThis.__counter = (globalThis.__counter || 0) + 1;
+          return globalThis.__injected;
         },
         { timeout: 0, polling: 10 }
       );
-      await page.waitForFunction(() => window.__counter > 10);
-      await page.evaluate(() => (window.__injected = true));
+      await page.waitForFunction(() => globalThis.__counter > 10);
+      await page.evaluate(() => (globalThis.__injected = true));
       await watchdog;
     });
     it('should survive cross-process navigation', async () => {
@@ -302,7 +306,7 @@ describe('waittask specs', function () {
 
       let fooFound = false;
       const waitForFunction = page
-        .waitForFunction('window.__FOO === 1')
+        .waitForFunction('globalThis.__FOO === 1')
         .then(() => (fooFound = true));
       await page.goto(server.EMPTY_PAGE);
       expect(fooFound).toBe(false);
@@ -310,17 +314,17 @@ describe('waittask specs', function () {
       expect(fooFound).toBe(false);
       await page.goto(server.CROSS_PROCESS_PREFIX + '/grid.html');
       expect(fooFound).toBe(false);
-      await page.evaluate(() => (window.__FOO = 1));
+      await page.evaluate(() => (globalThis.__FOO = 1));
       await waitForFunction;
       expect(fooFound).toBe(true);
     });
     it('should survive navigations', async () => {
       const { page, server } = getTestState();
 
-      const watchdog = page.waitForFunction(() => window.__done);
+      const watchdog = page.waitForFunction(() => globalThis.__done);
       await page.goto(server.EMPTY_PAGE);
       await page.goto(server.PREFIX + '/consolelog.html');
-      await page.evaluate(() => (window.__done = true));
+      await page.evaluate(() => (globalThis.__done = true));
       await watchdog;
     });
   });
@@ -594,7 +598,9 @@ describe('waittask specs', function () {
       await page
         .waitForSelector('.zombo', { timeout: 10 })
         .catch((error_) => (error = error_));
-      expect(error.stack).toContain('waittask.spec.js');
+      expect(error.stack).toContain('waiting for selector ".zombo" failed');
+      // The extension is ts here as Mocha maps back via sourcemaps.
+      expect(error.stack).toContain('waittask.spec.ts');
     });
   });
 
diff --git a/test/worker.spec.js b/test/worker.spec.ts
similarity index 85%
rename from test/worker.spec.js
rename to test/worker.spec.ts
index fb495f1eaa5b2..86aba8ca28950 100644
--- a/test/worker.spec.js
+++ b/test/worker.spec.ts
@@ -14,13 +14,16 @@
  * limitations under the License.
  */
 
-const expect = require('expect');
-const {
+import expect from 'expect';
+import {
   getTestState,
   setupTestBrowserHooks,
   setupTestPageAndContextHooks,
-} = require('./mocha-utils');
-const utils = require('./utils');
+  describeFailsFirefox,
+} from './mocha-utils';
+import utils from './utils';
+import { WebWorker } from '../src/common/WebWorker';
+import { ConsoleMessage } from '../src/common/ConsoleMessage';
 const { waitEvent } = utils;
 
 describeFailsFirefox('Workers', function () {
@@ -36,7 +39,7 @@ describeFailsFirefox('Workers', function () {
     const worker = page.workers()[0];
     expect(worker.url()).toContain('worker.js');
 
-    expect(await worker.evaluate(() => self.workerFunction())).toBe(
+    expect(await worker.evaluate(() => globalThis.workerFunction())).toBe(
       'worker function result'
     );
 
@@ -46,7 +49,7 @@ describeFailsFirefox('Workers', function () {
   it('should emit created and destroyed events', async () => {
     const { page } = getTestState();
 
-    const workerCreatedPromise = new Promise((x) =>
+    const workerCreatedPromise = new Promise<WebWorker>((x) =>
       page.once('workercreated', x)
     );
     const workerObj = await page.evaluateHandle(
@@ -81,7 +84,9 @@ describeFailsFirefox('Workers', function () {
   it('should have JSHandles for console logs', async () => {
     const { page } = getTestState();
 
-    const logPromise = new Promise((x) => page.on('console', x));
+    const logPromise = new Promise<ConsoleMessage>((x) =>
+      page.on('console', x)
+    );
     await page.evaluate(
       () => new Worker(`data:text/javascript,console.log(1,2,3,this)`)
     );
@@ -95,7 +100,7 @@ describeFailsFirefox('Workers', function () {
   it('should have an execution context', async () => {
     const { page } = getTestState();
 
-    const workerCreatedPromise = new Promise((x) =>
+    const workerCreatedPromise = new Promise<WebWorker>((x) =>
       page.once('workercreated', x)
     );
     await page.evaluate(
@@ -107,7 +112,7 @@ describeFailsFirefox('Workers', function () {
   it('should report errors', async () => {
     const { page } = getTestState();
 
-    const errorPromise = new Promise((x) => page.on('pageerror', x));
+    const errorPromise = new Promise<Error>((x) => page.on('pageerror', x));
     await page.evaluate(
       () =>
         new Worker(`data:text/javascript, throw new Error('this is my error');`)
diff --git a/tsconfig.json b/tsconfig.json
index da1d0b244affc..8b25d93823ed2 100644
--- a/tsconfig.json
+++ b/tsconfig.json
@@ -8,7 +8,8 @@
     "module": "CommonJS",
     "declaration": true,
     "declarationMap": true,
-    "esModuleInterop": true
+    "esModuleInterop": true,
+    "resolveJsonModule": true
   },
   "include": [
     "src"
diff --git a/utils/testserver/index.js b/utils/testserver/index.js
index a65910217d791..7d21009c94d14 100644
--- a/utils/testserver/index.js
+++ b/utils/testserver/index.js
@@ -1,3 +1,5 @@
+// @ts-nocheck
+
 /**
  * Copyright 2017 Google Inc. All rights reserved.
  *
@@ -26,6 +28,11 @@ const fulfillSymbol = Symbol('fullfil callback');
 const rejectSymbol = Symbol('reject callback');
 
 class TestServer {
+  PORT = undefined;
+  PREFIX = undefined;
+  CROSS_PROCESS_PREFIX = undefined;
+  EMPTY_PAGE = undefined;
+
   /**
    * @param {string} dirPath
    * @param {number} port