chore: move assert into its own module (#6021)

A lot of the helpers in `helpers.ts` are heavily bound to NodeJS and at
the moment we're trying to make the `Connection` class be able to run in
multiple environments. Its only remaining Node dependency was its
reliance on `helpers.ts`, which it only needed for `assert`.

This is a useful change also because `helpers.ts` is quite large and
full of functions that do different things; I think we can name them
better and move them into modules with a specific purpose rather than a
generic `"helpers"` dumping ground.

Once this change lands `Connection` should be usable in the browser.

src/Browser.ts

@@ -14,7 +14,8 @@
  * limitations under the License.
  */
 
-import { helper, assert } from './helper';
+import { assert } from './assert';
+import { helper } from './helper';
 import { Target } from './Target';
 import { EventEmitter } from './EventEmitter';
 import { Events } from './Events';

src/BrowserFetcher.ts

@@ -28,8 +28,8 @@ import removeRecursive from 'rimraf';
 import * as URL from 'url';
 import ProxyAgent from 'https-proxy-agent';
 import { getProxyForUrl } from 'proxy-from-env';
-
-import { helper, assert } from './helper';
+import { assert } from './assert';
+import { helper } from './helper';
 const debugFetcher = debug(`puppeteer:fetcher`);
 
 const downloadURLs = {

src/Connection.ts

@@ -13,7 +13,7 @@
  * See the License for the specific language governing permissions and
  * limitations under the License.
  */
-import { assert } from './helper';
+import { assert } from './assert';
 import { Events } from './Events';
 import debug from 'debug';
 const debugProtocolSend = debug('puppeteer:protocol:SEND ►');

src/Coverage.ts

@@ -14,7 +14,8 @@
  * limitations under the License.
  */
 
-import { helper, debugError, assert, PuppeteerEventListener } from './helper';
+import { assert } from './assert';
+import { helper, debugError, PuppeteerEventListener } from './helper';
 import Protocol from './protocol';
 import { CDPSession } from './Connection';
 

src/DOMWorld.ts

@@ -15,7 +15,8 @@
  */
 
 import * as fs from 'fs';
-import { helper, assert } from './helper';
+import { assert } from './assert';
+import { helper } from './helper';
 import { LifecycleWatcher, PuppeteerLifeCycleEvent } from './LifecycleWatcher';
 import { TimeoutError } from './Errors';
 import { JSHandle, ElementHandle } from './JSHandle';

src/Dialog.ts

@@ -14,7 +14,7 @@
  * limitations under the License.
  */
 
-import { assert } from './helper';
+import { assert } from './assert';
 import { CDPSession } from './Connection';
 import Protocol from './protocol';
 

src/ExecutionContext.ts

@@ -14,7 +14,8 @@
  * limitations under the License.
  */
 
-import { helper, assert } from './helper';
+import { assert } from './assert';
+import { helper } from './helper';
 import { createJSHandle, JSHandle, ElementHandle } from './JSHandle';
 import { CDPSession } from './Connection';
 import { DOMWorld } from './DOMWorld';

src/FileChooser.ts

@@ -16,7 +16,7 @@
 
 import { ElementHandle } from './JSHandle';
 import Protocol from './protocol';
-import { assert } from './helper';
+import { assert } from './assert';
 
 export class FileChooser {
   private _element: ElementHandle;

src/FrameManager.ts

@@ -15,7 +15,8 @@
  */
 
 import { EventEmitter } from './EventEmitter';
-import { helper, assert, debugError } from './helper';
+import { assert } from './assert';
+import { helper, debugError } from './helper';
 import { Events } from './Events';
 import { ExecutionContext, EVALUATION_SCRIPT_URL } from './ExecutionContext';
 import { LifecycleWatcher, PuppeteerLifeCycleEvent } from './LifecycleWatcher';

src/HTTPRequest.ts

@@ -16,7 +16,8 @@
 import { CDPSession } from './Connection';
 import { Frame } from './FrameManager';
 import { HTTPResponse } from './HTTPResponse';
-import { helper, assert, debugError } from './helper';
+import { assert } from './assert';
+import { helper, debugError } from './helper';
 import Protocol from './protocol';
 
 export class HTTPRequest {

src/Input.ts

@@ -14,7 +14,7 @@
  * limitations under the License.
  */
 
-import { assert } from './helper';
+import { assert } from './assert';
 import { CDPSession } from './Connection';
 import { keyDefinitions, KeyDefinition, KeyInput } from './USKeyboardLayout';
 

src/JSHandle.ts

@@ -14,7 +14,8 @@
  * limitations under the License.
  */
 
-import { helper, assert, debugError } from './helper';
+import { assert } from './assert';
+import { helper, debugError } from './helper';
 import { ExecutionContext } from './ExecutionContext';
 import { Page } from './Page';
 import { CDPSession } from './Connection';

src/Launcher.ts

@@ -23,7 +23,8 @@ import * as fs from 'fs';
 import { BrowserFetcher } from './BrowserFetcher';
 import { Connection } from './Connection';
 import { Browser } from './Browser';
-import { helper, assert, debugError } from './helper';
+import { assert } from './assert';
+import { helper, debugError } from './helper';
 import { ConnectionTransport } from './ConnectionTransport';
 import { WebSocketTransport } from './WebSocketTransport';
 import { BrowserRunner } from './launcher/BrowserRunner';

src/LifecycleWatcher.ts

@@ -14,7 +14,8 @@
  * limitations under the License.
  */
 
-import { helper, assert, PuppeteerEventListener } from './helper';
+import { assert } from './assert';
+import { helper, PuppeteerEventListener } from './helper';
 import { Events } from './Events';
 import { TimeoutError } from './Errors';
 import { FrameManager, Frame } from './FrameManager';

src/NetworkManager.ts

@@ -14,7 +14,8 @@
  * limitations under the License.
  */
 import { EventEmitter } from './EventEmitter';
-import { helper, assert, debugError } from './helper';
+import { assert } from './assert';
+import { helper, debugError } from './helper';
 import Protocol from './protocol';
 import { Events } from './Events';
 import { CDPSession } from './Connection';

src/Page.ts

@@ -24,7 +24,8 @@ import { EmulationManager } from './EmulationManager';
 import { Frame, FrameManager } from './FrameManager';
 import { Keyboard, Mouse, Touchscreen, MouseButtonInput } from './Input';
 import { Tracing } from './Tracing';
-import { helper, debugError, assert } from './helper';
+import { assert } from './assert';
+import { helper, debugError } from './helper';
 import { Coverage } from './Coverage';
 import { WebWorker } from './WebWorker';
 import { Browser, BrowserContext } from './Browser';

src/Tracing.ts

@@ -13,7 +13,8 @@
  * See the License for the specific language governing permissions and
  * limitations under the License.
  */
-import { helper, assert } from './helper';
+import { assert } from './assert';
+import { helper } from './helper';
 import { CDPSession } from './Connection';
 
 interface TracingOptions {

src/assert.ts

@@ -0,0 +1,24 @@
+/**
+ * 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.
+ */
+
+/**
+ * Asserts that the given value is truthy.
+ * @param value
+ * @param message - the error message to throw if the value is not truthy.
+ */
+export const assert = (value: unknown, message?: string): void => {
+  if (!value) throw new Error(message);
+};

src/helper.ts

@@ -20,17 +20,14 @@ import { CDPSession } from './Connection';
 import { promisify } from 'util';
 import Protocol from './protocol';
 import { CommonEventEmitter } from './EventEmitter';
+import { assert } from './assert';
 
 const openAsync = promisify(fs.open);
 const writeAsync = promisify(fs.write);
 const closeAsync = promisify(fs.close);
 
 export const debugError = debug('puppeteer:error');
 
-export function assert(value: unknown, message?: string): void {
-  if (!value) throw new Error(message);
-}
-
 interface AnyClass {
   prototype: object;
 }

src/launcher/BrowserRunner.ts

@@ -18,7 +18,8 @@ import debug from 'debug';
 
 import removeFolder from 'rimraf';
 import * as childProcess from 'child_process';
-import { helper, assert, debugError } from '../helper';
+import { assert } from '../assert';
+import { helper, debugError } from '../helper';
 import { LaunchOptions } from './LaunchOptions';
 import { Connection } from '../Connection';
 import { WebSocketTransport } from '../WebSocketTransport';