Add webp to screenshot options

docs/api.md

@@ -2177,7 +2177,7 @@ Shortcut for [page.mainFrame().executionContext().queryObjects(prototypeHandle)]
 
 - `options` <[Object]> Options object which might have the following properties:
   - `path` <[string]> The file path to save the image to. The screenshot type will be inferred from file extension. If `path` is a relative path, then it is resolved relative to [current working directory](https://nodejs.org/api/process.html#process_process_cwd). If no path is provided, the image won't be saved to the disk.
-  - `type` <[string]> Specify screenshot type, can be either `jpeg` or `png`. Defaults to 'png'.
+  - `type` <[string]> Specify screenshot type, can be either `jpeg`, `png` or `webp`. Defaults to 'png'.
   - `quality` <[number]> The quality of the image, between 0-100. Not applicable to `png` images.
   - `fullPage` <[boolean]> When true, takes a screenshot of the full scrollable page. Defaults to `false`.
   - `clip` <[Object]> An object which specifies clipping region of the page. Should have the following fields:

src/common/Page.ts

@@ -31,7 +31,7 @@ import {
 } from './FrameManager.js';
 import { Keyboard, Mouse, Touchscreen, MouseButton } from './Input.js';
 import { Tracing } from './Tracing.js';
-import { assert } from './assert.js';
+import { assert, assertNever } from './assert.js';
 import { helper, debugError } from './helper.js';
 import { Coverage } from './Coverage.js';
 import { WebWorker } from './WebWorker.js';
@@ -157,7 +157,7 @@ export interface ScreenshotOptions {
   /**
    * @defaultValue 'png'
    */
-  type?: 'png' | 'jpeg';
+  type?: 'png' | 'jpeg' | 'webp';
   /**
    * The file path to save the image to. The screenshot type will be inferred
    * from file extension. If path is a relative path, then it is resolved
@@ -2560,10 +2560,10 @@ export class Page extends EventEmitter {
     // because it may be a 0-length file with no extension created beforehand
     // (i.e. as a temp file).
     if (options.type) {
-      assert(
-        options.type === 'png' || options.type === 'jpeg',
-        'Unknown options.type value: ' + options.type
-      );
+      const type = options.type;
+      if (type !== 'png' && type !== 'jpeg' && type !== 'webp') {
+        assertNever(type, 'Unknown options.type value: ' + type);
+      }
       screenshotType = options.type;
     } else if (options.path) {
       const filePath = options.path;
@@ -2573,6 +2573,7 @@ export class Page extends EventEmitter {
       if (extension === 'png') screenshotType = 'png';
       else if (extension === 'jpg' || extension === 'jpeg')
         screenshotType = 'jpeg';
+      else if (extension === 'webp') screenshotType = 'webp';
       assert(
         screenshotType,
         `Unsupported screenshot type for extension \`.${extension}\``
@@ -2643,7 +2644,7 @@ export class Page extends EventEmitter {
   }
 
   private async _screenshotTask(
-    format: 'png' | 'jpeg',
+    format: Protocol.Page.CaptureScreenshotRequestFormat,
     options?: ScreenshotOptions
   ): Promise<Buffer | string> {
     await this._client.send('Target.activateTarget', {
@@ -2682,7 +2683,7 @@ export class Page extends EventEmitter {
       }
     }
     const shouldSetDefaultBackground =
-      options.omitBackground && format === 'png';
+      options.omitBackground && (format === 'png' || format === 'webp');
     if (shouldSetDefaultBackground) {
       await this._setTransparentBackgroundColor();
     }

src/common/assert.ts

@@ -22,3 +22,7 @@
 export const assert = (value: unknown, message?: string): void => {
   if (!value) throw new Error(message);
 };
+
+export const assertNever = (value: never, message?: string): void => {
+  if (value) throw new Error(message);
+};

test/screenshot.spec.ts

@@ -142,6 +142,17 @@ describe('Screenshots', function () {
       });
       expect(screenshot).toBeGolden('white.jpg');
     });
+    itFailsFirefox('should work with webp', async () => {
+      const { page, server } = getTestState();
+
+      await page.setViewport({ width: 100, height: 100 });
+      await page.goto(server.PREFIX + '/grid.html');
+      const screenshot = await page.screenshot({
+        type: 'webp',
+      });
+
+      expect(screenshot).toBeInstanceOf(Buffer);
+    });
     it('should work with odd clip size on Retina displays', async () => {
       const { page } = getTestState();