Two days after releasing the stable version of Chrome 38, Google has pushed out Chrome 39 beta for Windows, Mac, and Linux (though most improvements will also apply to Android and Chrome OS). This is mainly a developer release: There are no new features for consumers as far as we can tell.

Here are the developer additions Google wants to highlight:

  • JavaScript Generators: ES6 Generators allow developers to create iterators that pause their execution after yielding a value, and resume again when later invoked. The goal is to simplify the process of developing asynchronous code and reduce dependence on callback functions.
  • Web Animation Playback Control: Web Animations, a new API that shipped in Chrome 36 with basic support, now has playback control, including the methods play(), pause(), and reverse(), as well as the ability to jump to a specific point in an animation’s timeline.
  • Web Application Manifests: Starting in Chrome 39, Manifests let developers wrap metadata about a Web application into a single file, reducing duplication and saving a bit of bandwidth. Adding apps to the homescreen is as easy as defining a title, landing page, default orientation, and multiple icons depending on size and screen density.
  • The Beacon API lets developers queue asynchronous network requests that will be sent regardless of whether the user navigates to a new page.
  • Scroll offsets (scrollTop, scrollLeft) now return high-precision fractional values in preparation for high-DPI support.
  • XMLHttpRequest progress event properties position and totalSize are now deprecated in favor of the loaded and total properties.

It’s worth noting that while the changelog mentions “64-bit support for Mac,” this actually first arrived in Chrome 38 beta, so it’s not new to the beta channel. Google is planning to release Chrome 39 in November, and unlike on Windows where 32-bit and 64-bit versions will both continue to be available, from that point on Chrome for Mac will only be available in 64-bit.