New in Chrome 64

• Support for ResizeObservers, will notify you when an element's content rectangle has changed its size.
• Modules can now access to host specific metadata with import.meta.
• The pop-up blocker gets strong.
• window.alert() no longer changes focus.

And there's plenty more!

I'm Pete LePage. Let's dive in and see what's new for developers in Chrome 64!

Want the full list of changes? Check out the Chromium source repository change list.

# ResizeObserver

Tracking when an element's size changes can be a bit of a pain. Most likely, you'll attach a listener to the document's resize event, then call getBoundingClientRect or getComputedStyle. But, both of those can cause layout thrashing.

And what if the browser window didn't change size, but a new element was added to the document? Or you added display: none to an element? Both of those can change the size of other elements within the page.

ResizeObserver notifies you whenever an element's size changes, and provides the new height and width of the element, reducing the risk of layout thrashing.

Like other Observers, using it is pretty simple, create a ResizeObserver object and pass a callback to the constructor. The callback will be given an array of ResizeOberverEntries–one entry per observed element–which contain the new dimensions for the element.

const ro = new ResizeObserver( entries => {
  for (const entry of entries) {
    const cr = entry.contentRect;
    console.log('Element:', entry.target);
    console.log(`Element size: ${cr.width}px × ${cr.height}px`);
    console.log(`Element padding: ${cr.top}px ; ${cr.left}px`);
  }
});

// Observe one or multiple elements
ro.observe(someElement);

Check out ResizeObserver: It's like document.onresize for Elements for more details and real world examples.

# Improved Pop-up Blocker

I hate tab-unders. You know them, it's when a page opens a pop-up to some destination AND navigates the page. Usually one of them is an ad or something that you didn't want.

Starting in Chrome 64, these type of navigations will be blocked, and Chrome will show some native UI to the user - allowing them to follow the redirect if they want.

# import.meta

When writing JavaScript modules, you often want access to host-specific metadata about the current module. Chrome 64 now supports the import.meta property within modules and exposes the URL for the module as import.meta.url.

This is really helpful when you want to resolve resources relative to the module file as opposed to the current HTML document.

# And more!

These are just a few of the changes in Chrome 64 for developers, of course, there's plenty more.

• Chrome now supports named captures and Unicode property escapes in regular expressions.
• The default preload value for <audio> and <video> elements is now metadata. This brings Chrome in line with other browsers and helps to reduce bandwidth and resource usage by only loading the metadata and not the media itself.
• You can now use Request.prototype.cache to view the cache mode of a Request and determine whether a request is a reload request.
• Using the Focus Management API, you can now focus an element without scrolling to it with the preventScroll attribute.

# window.alert()

Oh, and one more! While this isn't really a "developer feature", it makes me happy. window.alert() no longer brings a background tab to the foreground! Instead, the alert will be shown when the user switches to back to that tab.

No more random tab switching because something fired a window.alert on me. I'm looking at you old Google Calendar.

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I'm Pete LePage, and as soon as Chrome 65 is released, I'll be right here to tell you -- what's new in Chrome!