Chromium Blog
News and developments from the open source browser project
Chrome 49 Beta: CSS custom properties, background sync with service workers, and new ES2015 features
Tuesday, February 2, 2016
Unless otherwise noted, changes described below apply to the newest Chrome
Beta
channel release for Android, Chrome OS, Linux, Mac, and Windows.
CSS custom properties
Modern websites often have CSS files with repeated values, such as a few colors reused throughout the page in a color scheme. Altering this data can be tedious and error-prone, since it’s scattered throughout one or more CSS files.
To improve this, Chrome now supports
CSS custom properties
, allowing developers to define property variables in CSS without using external frameworks. Developers can then use the
var() function
to
reference these custom properties
anywhere in the document.
Changing a custom property can update multiple components in a website
CSS custom properties also inherit across
shadow roots
, so a web component can provide a “style API” that makes it possible to tweak and theme the component without knowing about its internals. The Polymer library uses this platform feature to
simplify customizing components
.
Background sync with service workers
Previously, sites could lose local changes or become out of sync if a user didn’t stay on the site until updates could be sent over the network. For example, an email client might lose a pending message if the user hit "send" and quickly navigated away. The new
Background Sync API
improves
networking reliability by allowing
service workers to schedule
a one-off sync of a user’s local changes
when the device next connects to the network, even if the site isn’t open.
Improved ECMAScript 2015 support
The
ES2015 specification
(ES6) is a major update to JavaScript that allows developers to write application logic that is more legible, powerful, and memory efficient. The
latest version of Chrome’s V8 engine
has
91% JavaScript ES2015 feature support
. Developers can now use
destructuring
and
default parameters
to avoid boilerplate code when extracting data from arrays and objects or when
setting function parameter defaults
.
Proxy objects
and the
Reflect API
can
customize previously hidden object behavior such as property lookup and assignment
. The latest version of Chrome also makes block-level constructs such as
class
and
let
available outside of
strict mode
.
Keygen and application/x-x509-user-cert
The
<keygen> element
is used to generate a key-pair as part of an HTML form. While this can be used to enhance user security, <keygen> and user certificates sent with the MIME type of application/x-x509-user-cert can be exploited to disrupt a user’s secure communication, interfere with the functioning of their devices, or track the user without consent. Going forward, <keygen> will return an empty string by default and user certificates sent with the MIME type of application/x-x509-user-cert will no longer be automatically downloaded and installed.
Other features in this release
With user consent, sites can
record audio and video
without relying on plugins by using the new
MediaRecorder API
.
Developers can now
control how fonts load
using
CSS font-display
, improving page load speed.
Sites can now detect which service worker client initiated a fetch request and return a specialized response using the
FetchEvent.clientID attribute
.
Chrome now
animates scrolling
for discrete scrolling devices like mouse wheels, allowing for a
smoother user experience
.
Chrome now more strictly
protects secure cookies
and allows developers to identify secure cookies using
cookie prefixes
.
Sites can now prevent media from playing remotely
using the disableRemotePlayback attribute
as part of the
Remote Playback API
.
Event.timeStamp is now a
DOMHighResTimeStamp
instead of a
DOMTimeStamp
, allowing for high-precision scroll latency and
pointer velocity measurements
.
Promise rejection handling can now be tracked using the
UnhandledRejection and RejectionHandled events
.
Developers can now
interact with the GET parameters of a URL
more easily using
URLSearchParams
.
The
WebAudio API
now supports
IIR Filters
,
OfflineAudioContext.suspend() and resume()
, and promises in
DecodeAudioData
.
WindowClient.navigate()
allows
service workers to navigate controlled windows
to a new URL.
Sites can detect if a user has requested reduced data usage and respond with a lighter experience by checking the
Save-Data header field
.
Mi
nor changes
Chrome’s
content security policy
now matches ‘script-src http:’ to both HTTP and HTTPS, preventing developers from accidentally rejecting secure resources.
The
Request.mode
enum of the
Fetch API
now
supports a navigate mode
, improving spec compliance.
Developers now have the option to
ignore case
when matching attribute selectors.
Developers can now create pop-ups that don’t expose which page opened them using
'rel=noopener'
.
addEventListener() and removeEventListener()
now require their first two arguments and can have the "capture" option specified using dictionary syntax, improving spec compliance and flexibility.
Chromium now supports the standardized version of
ChaCha-Poly1305 cipher suites
in TLS.
Navigator.getStorageUpdates() has been removed as it is no longer in the
Navigator spec
.
MouseEvent.webkitMovementX/Y has been removed in favor of the
unprefixed version
.
initTouchEvent
has been deprecated in favor of the
TouchEvent constructor
to improve spec compliance and will be removed altogether in Chrome 53.
Object.observe() has been deprecated as it is
no longer on the standardization track
and will be removed in a future release.
The
getComputedStyle(e).cssX
behaviour has been deprecated since it was not a part of the formal
spec
.
Some non-standard uses of RTCPeerConnection legacy methods have been deprecated to enable promise-based implementation of the
WebRTC spec
.
Document.defaultCharset
has been deprecated to improve spec compliance.
Posted by Josh Karlin, Syncing Samurai
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