Chromium Blog
News and developments from the open source browser project
Chrome 52 Beta: CSS containment, simpler performance measurement, streamable responses from service workers, and more options for web push
2016年6月10日金曜日
Unless otherwise noted, changes described below apply to the newest Chrome
Beta
channel release for Android, Chrome OS, Linux, Mac, and Windows.
CSS Containment
Rich, interactive experiences are a cornerstone of the web, but can sometimes take a long time to render due to their complexity. Currently, Chrome improves rendering performance by using heuristics to determine which parts of a page have changed. Only sections that have changed are updated instead of rendering the entire page 60 times per second. However, because elements can display outside the bounds of their parents, it is possible that changes to one element could affect elements anywhere else in the document. This dramatically increases the number of elements that Chrome must consider while rendering.
New in this release, the CSS
contain
property allows developers to
prevent an element’s children from displaying outside of its bounds
. When an element updates, this guarantee allows Chrome to ignore any element outside the parent node during rendering, leading to faster rendering times.
Performance Observer
Collecting accurate real-user measurement (RUM) data is critical to detecting performance problems and regressions that may hurt the user experience of a site. Chrome's DevTools allow local site testing, but measuring how a site performs for real users with varied devices can be challenging. The latest version of Chrome supports the
PerformanceObserver
API, which enables a
simple and performant way to collect RUM data
at runtime. Instead of polling for updates,
sites can declare which metrics they’re interested in
. The browser notifies the site when new data points for those metrics become available.
Service Worker Responses Powered by ReadableStreams
Streaming HTTP responses allow browsers to progressively render earlier portions of a large HTML document before the entire response is available. The latest version of Chrome
improves service workers by adding streaming support
. Sites can use the
Streams API
to construct streamable
Response
objects by passing a
ReadableStream
to the Response constructor.
Offline Wikipedia client
demonstrates the speed benefits of readable streams.
Web Push Protocol and VAPID Support
Push notifications
have unlocked a new level of re-engagement for web apps, but until now developers have had to use proprietary push message delivery services and different APIs for different browsers. Chrome now supports
VAPID
, an open standard to authenticate a site’s server with a push service. When using VAPID, sites are given a
Firebase Cloud Messaging
endpoint, which supports the cross-browser
web push protocol
.
Other features in this release
Chrome now pauses animations while showing modal dialog boxes.
HTTP
alternative services
allow sites to specify additional origins that can be used to reach a certain resource, enabling easier protocol upgrades and load balancing.
ImageBitmaps
can be created more easily using
ImageBitmapOptions
to specify configurations on construction.
Sites can now free the memory consumed by an
ImageBitmap
using
ImageBitmap.close()
.
Chrome now supports
OpenType
small capitals and easier styling of numbers using the
font-variant-caps
and
font-variant-numeric
properties.
Touch gestures
inside a cross-origin iframe can no longer trigger popups unless they correspond to a tap gesture, preventing accidental pop-ups during scrolling.
Now only secure origins can
create or delete secure cookies
on Chrome for Android.
The latest version of Chrome supports
-webkit-appearance:none
which disables the default rendering of HTML5
meter
elements and allows easier custom CSS styling.
The
unsafe-dynamic
Content Security Policy expression allows sites to use single-use or hash-based whitelists to verify script sources, making it easier to
protect against cross-origin scripting attacks
.
Sites can
now use the Fetch API
to programmatically
set the referrer policy
for a
request
.
CanvasRenderingContext2D
now supports the
filter
attribute, allowing sites to apply effects to primitives drawn to the canvas.
Sites can now test whether or not a key exists within the bounds of an
IDBKeyRange
using
IDBKeyRange.includes()
.
The
HTMLMediaElement.srcObject
attribute simplifies associating a
MediaStream
with a media element.
AudioParam
now supports the read-only
min
and
max
attributes
to simplify introspection.
RTCCertificates
can now be stored in IndexedDB.
PannerNode
and
AudioListener
now support automation methods, allowing smooth audio transitions.
Stylesheets can now specify alpha values for colors using
eight- and four-bit hexadecimal values
instead of the longer
rgba()
syntax.
Sites
can now experiment
with
persistent storage
as an
origin trial
, allowing a site to disable automatic storage clearing when bookmarked.
Multiple WebVTT tracks will now be presented as
user options
in the default media controls, enabling language selection for captions and subtitles.
postMessage
overrides of the form
postMessage(message,transferables,targetOrigin)
have been deprecated.
The
MediaStream
ended event and the corresponding onended attribute have been deprecated.
The
web app manifest
icons
entry no longer supports the density property.
The
DynamicsCompressorNode.reduction
attribute is now a
readonly float
instead of an
AudioParam
.
flexbox
children with
position:absolute
will now be
positioned using justify and align
if the element does not have a
left:
,
right:
,
top:
,
or bottom:
position specified.
requestAutocomplete()
has been
deprecated and removed
due to low usage numbers.
X-Frame-Option
will no longer be supported in the
meta
tag to support a more secure implementation.
Invalid values for
track-kind
are now treated as
metadata
instead of
subtitles
to improve media behavior in older user agents.
Posted by Shubhie Panicker, Performance Powerhouse
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