document.webkitFullscreenElement always undefined

[samuelsh]

• Puppeteer version: 1.4
• Platform / OS version: MacOS Sierra
• URLs (if applicable): https://kabbalahmedia.info/en/lessons/daily/latest?language=en
• Node.js version: 9.0.8

Following code won't work, webkitFullscreenElement is undefined even if Full Screen mode is set:

isFullScreen: async function (page) {
        const executionContext = await page.mainFrame().executionContext();
        const fullscreenElement =  await executionContext.evaluate(() => {
            return document.webkitFullscreenElement
        });
        console.debug('isFullScreen: ' + fullscreenElement);
        return !!(fullscreenElement && fullscreenElement.nodeName === 'video');
    }

[aslushnikov]

@samuelsh You should use evaluateHandle instead of evaluate.

It's unfortunate that page.evaluate doesn't throw an error in this case; this will be fixed in the next major release: #2079