feat(api): add page.emulateMedia{Type,Features}

docs/api.md

@@ -108,7 +108,9 @@
   * [page.coverage](#pagecoverage)
   * [page.deleteCookie(...cookies)](#pagedeletecookiecookies)
   * [page.emulate(options)](#pageemulateoptions)
-  * [page.emulateMedia(mediaType)](#pageemulatemediamediatype)
+  * [page.emulateMedia(type)](#pageemulatemediatype)
+  * [page.emulateMediaFeatures(features)](#pageemulatemediafeaturesfeatures)
+  * [page.emulateMediaType(type)](#pageemulatemediatypetype)
   * [page.evaluate(pageFunction[, ...args])](#pageevaluatepagefunction-args)
   * [page.evaluateHandle(pageFunction[, ...args])](#pageevaluatehandlepagefunction-args)
   * [page.evaluateOnNewDocument(pageFunction[, ...args])](#pageevaluateonnewdocumentpagefunction-args)
@@ -1276,10 +1278,78 @@ puppeteer.launch().then(async browser => {
 
 List of all available devices is available in the source code: [DeviceDescriptors.js](https://github.com/GoogleChrome/puppeteer/blob/master/lib/DeviceDescriptors.js).
 
-#### page.emulateMedia(mediaType)
-- `mediaType` <?[string]> Changes the CSS media type of the page. The only allowed values are `'screen'`, `'print'` and `null`. Passing `null` disables media emulation.
+#### page.emulateMedia(type)
+- `type` <?[string]> Changes the CSS media type of the page. The only allowed values are `'screen'`, `'print'` and `null`. Passing `null` disables CSS media emulation.
 - returns: <[Promise]>
 
+**Note:** This method is deprecated, and only kept around as an alias for backwards compatibility. Use [`page.emulateMediaType(type)`](#pageemulatemediatypetype) instead.
+
+#### page.emulateMediaFeatures(features)
+- `features` <?[Array]<[Object]>> Given an array of media feature objects, emulates CSS media features on the page. Each media feature object must have the following properties:
+  - `name` <[string]> The CSS media feature name. Supported names are `'prefers-colors-scheme'` and `'prefers-reduced-motion'`.
+  - `value` <[string]> The value for the given CSS media feature.
+- returns: <[Promise]>
+
+```js
+await page.emulateMediaFeatures([{ name: 'prefers-color-scheme', value: 'dark' }]);
+await page.evaluate(() => matchMedia('(prefers-color-scheme: dark)').matches));
+// → true
+await page.evaluate(() => matchMedia('(prefers-color-scheme: light)').matches));
+// → false
+await page.evaluate(() => matchMedia('(prefers-color-scheme: no-preference)').matches));
+// → false
+
+await page.emulateMediaFeatures([{ name: 'prefers-reduced-motion', value: 'reduce' }]);
+await page.evaluate(() => matchMedia('(prefers-reduced-motion: reduce)').matches));
+// → true
+await page.evaluate(() => matchMedia('(prefers-color-scheme: no-preference)').matches));
+// → false
+
+await page.emulateMediaFeatures([{ name: 'prefers-reduced-motion', value: 'reduce' }]);
+await page.evaluate(() => matchMedia('(prefers-reduced-motion: reduce)').matches));
+// → true
+await page.evaluate(() => matchMedia('(prefers-color-scheme: no-preference)').matches));
+// → false
+
+await page.emulateMediaFeatures([
+  { name: 'prefers-color-scheme', value: 'dark' },
+  { name: 'prefers-reduced-motion', value: 'reduce' },
+]);
+await page.evaluate(() => matchMedia('(prefers-color-scheme: dark)').matches));
+// → true
+await page.evaluate(() => matchMedia('(prefers-color-scheme: light)').matches));
+// → false
+await page.evaluate(() => matchMedia('(prefers-color-scheme: no-preference)').matches));
+// → false
+await page.evaluate(() => matchMedia('(prefers-reduced-motion: reduce)').matches));
+// → true
+await page.evaluate(() => matchMedia('(prefers-color-scheme: no-preference)').matches));
+// → false
+```
+
+#### page.emulateMediaType(type)
+- `type` <?[string]> Changes the CSS media type of the page. The only allowed values are `'screen'`, `'print'` and `null`. Passing `null` disables CSS media emulation.
+- returns: <[Promise]>
+
+```js
+await page.evaluate(() => matchMedia('screen').matches));
+// → true
+await page.evaluate(() => matchMedia('print').matches));
+// → true
+
+await page.emulateMediaType('print');
+await page.evaluate(() => matchMedia('screen').matches));
+// → false
+await page.evaluate(() => matchMedia('print').matches));
+// → true
+
+await page.emulateMediaType(null);
+await page.evaluate(() => matchMedia('screen').matches));
+// → true
+await page.evaluate(() => matchMedia('print').matches));
+// → true
+```
+
 #### page.evaluate(pageFunction[, ...args])
 - `pageFunction` <[function]|[string]> Function to be evaluated in the page context
 - `...args` <...[Serializable]|[JSHandle]> Arguments to pass to `pageFunction`

experimental/puppeteer-firefox/lib/Page.js

@@ -150,11 +150,11 @@ class Page extends EventEmitter {
   }
 
   /**
-   * @param {?string} mediaType
+   * @param {?string} type
    */
-  async emulateMedia(mediaType) {
-    assert(mediaType === 'screen' || mediaType === 'print' || mediaType === null, 'Unsupported media type: ' + mediaType);
-    await this._session.send('Page.setEmulatedMedia', {media: mediaType || ''});
+  async emulateMediaType(type) {
+    assert(type === 'screen' || type === 'print' || type === null, 'Unsupported media type: ' + type);
+    await this._session.send('Page.setEmulatedMedia', {media: type || ''});
   }
 
   /**
@@ -747,6 +747,9 @@ class Page extends EventEmitter {
   }
 }
 
+// Expose alias for deprecated method.
+Page.prototype.emulateMedia = Page.prototype.emulateMediaType;
+
 class ConsoleMessage {
   /**
    * @param {string} type

lib/Page.js

@@ -801,11 +801,27 @@ class Page extends EventEmitter {
   }
 
   /**
-   * @param {?string} mediaType
+   * @param {?string} type
    */
-  async emulateMedia(mediaType) {
-    assert(mediaType === 'screen' || mediaType === 'print' || mediaType === null, 'Unsupported media type: ' + mediaType);
-    await this._client.send('Emulation.setEmulatedMedia', {media: mediaType || ''});
+  async emulateMediaType(type) {
+    assert(type === 'screen' || type === 'print' || type === null, 'Unsupported media type: ' + type);
+    await this._client.send('Emulation.setEmulatedMedia', {media: type || ''});
+  }
+
+  /**
+   * @param {?Array<MediaFeature>} features
+   */
+  async emulateMediaFeatures(features) {
+    if (features === null)
+      await this._client.send('Emulation.setEmulatedMedia', {features: null});
+    if (Array.isArray(features)) {
+      features.every(mediaFeature => {
+        const name = mediaFeature.name;
+        assert(/^prefers-(?:color-scheme|reduced-motion)$/.test(name), 'Unsupported media feature: ' + name);
+        return true;
+      });
+      await this._client.send('Emulation.setEmulatedMedia', {features: features});
+    }
   }
 
   /**
@@ -1116,6 +1132,9 @@ class Page extends EventEmitter {
   }
 }
 
+// Expose alias for deprecated method.
+Page.prototype.emulateMedia = Page.prototype.emulateMediaType;
+
 /**
  * @typedef {Object} PDFOptions
  * @property {number=} scale
@@ -1161,6 +1180,12 @@ class Page extends EventEmitter {
  * @property {string=} encoding
  */
 
+/**
+ * @typedef {Object} MediaFeature
+ * @property {string} name
+ * @property {string} value
+ */
+
 /** @type {!Set<string>} */
 const supportedMetrics = new Set([
   'Timestamp',

test/emulation.spec.js

@@ -98,20 +98,63 @@ module.exports.addTests = function({testRunner, expect, puppeteer}) {
   });
 
   describe('Page.emulateMedia', function() {
+    it('should be an alias for Page.emulateMediaType', async({page, server}) => {
+      expect(page.emulateMedia).toEqual(page.emulateMediaType);
+    });
+  });
+
+  describe('Page.emulateMediaType', function() {
     it('should work', async({page, server}) => {
-      expect(await page.evaluate(() => window.matchMedia('screen').matches)).toBe(true);
-      expect(await page.evaluate(() => window.matchMedia('print').matches)).toBe(false);
-      await page.emulateMedia('print');
-      expect(await page.evaluate(() => window.matchMedia('screen').matches)).toBe(false);
-      expect(await page.evaluate(() => window.matchMedia('print').matches)).toBe(true);
-      await page.emulateMedia(null);
-      expect(await page.evaluate(() => window.matchMedia('screen').matches)).toBe(true);
-      expect(await page.evaluate(() => window.matchMedia('print').matches)).toBe(false);
+      expect(await page.evaluate(() => matchMedia('screen').matches)).toBe(true);
+      expect(await page.evaluate(() => matchMedia('print').matches)).toBe(false);
+      await page.emulateMediaType('print');
+      expect(await page.evaluate(() => matchMedia('screen').matches)).toBe(false);
+      expect(await page.evaluate(() => matchMedia('print').matches)).toBe(true);
+      await page.emulateMediaType(null);
+      expect(await page.evaluate(() => matchMedia('screen').matches)).toBe(true);
+      expect(await page.evaluate(() => matchMedia('print').matches)).toBe(false);
     });
     it('should throw in case of bad argument', async({page, server}) => {
       let error = null;
-      await page.emulateMedia('bad').catch(e => error = e);
+      await page.emulateMediaType('bad').catch(e => error = e);
       expect(error.message).toBe('Unsupported media type: bad');
     });
   });
+
+  describe_fails_ffox('Page.emulateMediaFeatures', function() {
+    it('should work', async({page, server}) => {
+      await page.emulateMediaFeatures([
+        { name: 'prefers-reduced-motion', value: 'reduce' },
+      ]);
+      expect(await page.evaluate(() => matchMedia('(prefers-reduced-motion: reduce)').matches)).toBe(true);
+      expect(await page.evaluate(() => matchMedia('(prefers-reduced-motion: no-preference)').matches)).toBe(false);
+      await page.emulateMediaFeatures([
+        { name: 'prefers-color-scheme', value: 'light' },
+      ]);
+      expect(await page.evaluate(() => matchMedia('(prefers-color-scheme: light)').matches)).toBe(true);
+      expect(await page.evaluate(() => matchMedia('(prefers-color-scheme: dark)').matches)).toBe(false);
+      expect(await page.evaluate(() => matchMedia('(prefers-color-scheme: no-preference)').matches)).toBe(false);
+      await page.emulateMediaFeatures([
+        { name: 'prefers-color-scheme', value: 'dark' },
+      ]);
+      expect(await page.evaluate(() => matchMedia('(prefers-color-scheme: dark)').matches)).toBe(true);
+      expect(await page.evaluate(() => matchMedia('(prefers-color-scheme: light)').matches)).toBe(false);
+      expect(await page.evaluate(() => matchMedia('(prefers-color-scheme: no-preference)').matches)).toBe(false);
+      await page.emulateMediaFeatures([
+        { name: 'prefers-reduced-motion', value: 'reduce' },
+        { name: 'prefers-color-scheme', value: 'light' },
+      ]);
+      expect(await page.evaluate(() => matchMedia('(prefers-reduced-motion: reduce)').matches)).toBe(true);
+      expect(await page.evaluate(() => matchMedia('(prefers-reduced-motion: no-preference)').matches)).toBe(false);
+      expect(await page.evaluate(() => matchMedia('(prefers-color-scheme: light)').matches)).toBe(true);
+      expect(await page.evaluate(() => matchMedia('(prefers-color-scheme: dark)').matches)).toBe(false);
+      expect(await page.evaluate(() => matchMedia('(prefers-color-scheme: no-preference)').matches)).toBe(false);
+    });
+    it('should throw in case of bad argument', async({page, server}) => {
+      let error = null;
+      await page.emulateMediaFeatures([{ name: 'bad', value: '' }]).catch(e => error = e);
+      expect(error.message).toBe('Unsupported media feature: bad');
+    });
+  });
+
 };

test/test.js

@@ -73,6 +73,7 @@ beforeEach(async({server, httpsServer}) => {
 });
 
 const CHROMIUM_NO_COVERAGE = new Set([
+  'page.emulateMedia', // Legacy alias for `page.emulateMediaType`.
 ]);
 
 if (process.env.BROWSER === 'firefox') {