Chromium Blog
News and developments from the open source browser project
New JavaScript techniques for rapid page loads
2015年3月18日水曜日
Posted by Marja Hölttä and Daniel Vogelheim, Resident Loader Coders
Speed has always been one of Chrome's primary missions, ever since it was included as one of the
founding principles
in 2008. But speed is about more than just traditional Javascript benchmarks. Ideally
every
part of a user's interaction with a browser is fast, starting with loading web pages. Chrome is introducing two techniques called script streaming and code caching designed to reduce that painful waiting time spent staring at a white screen, especially on mobile devices.
Script streaming optimizes the parsing of JavaScript files. Previous versions of Chrome would download a script in full before beginning to parse it, which is a straightforward approach but doesn't fully utilize the CPU while waiting for the download to complete. Starting in version 41, Chrome parses
async and deferred scripts
on a separate thread as soon as the download has begun. This means that parsing can complete just milliseconds after the download has finished, and results in pages loading as much as 10% faster. It's particularly effective on large scripts and slow network connections.
Code caching is another new technique that helps speed up page loading, specifically on repeated visits to the same page. Normally, the V8 engine compiles the page’s JavaScript on every visit, turning it into instructions that a processor understands. This compiled code is then discarded once a user navigates away from the page as compiled code is highly dependent on the state and context of the machine at compilation time. Chrome 42 introduces an advanced technique of storing a local copy of the compiled code, so that when the user returns to the page the downloading, parsing, and compiling steps can all be skipped. Across all page loads, this allows Chrome to avoid about 40% of compile time and saves precious battery on mobile devices.
These are two examples of ways Chrome is improving page load time, but page load time is just one way to think about the performance of the browser. Stay tuned for more ways the Chromium project is pushing forward all aspects of performance on the web.
Chrome 42 Beta: Push Notifications, Promoting Add to Home Screen and ES6 Classes
2015年3月12日木曜日
Posted by John Mellor and Michael van Ouwerkerk, 'appiest Software Engineers in London
The newest Chrome
Beta
channel release includes support for ES6 Classes and several new features that allow developers to create more immersive web applications. Unless otherwise noted, changes described below apply to Chrome for Android, Windows, Mac, Linux and Chrome OS.
Push Notifications
This release includes two new APIs that together allow sites to
push native notifications to their users
even after the page is closed—provided the user has granted explicit permission.
After the user has granted permission, a developer can use
the new
Push API
to remotely wake up their
service worker
using
Google Cloud Messaging
. Once awake, the service worker may run JavaScript for a short period but in this release it is required at minimum to show a user-visible
notification
. Each notification includes a ‘Site Settings’ button, allowing users to easily disable notifications for a site.
Promoting Add to Home Screen
Chrome 32 introduced the ability for Android users to add home screen shortcuts to their favorite websites via a
menu item
. In this release, users who frequently visit a high-quality web app will see a banner that allows them to add the site to their home screen in one tap.
Sites that wish to
take advantage of this new feature
must meet eligibility criteria that ensure that users have a good experience when launching sites from the home screen, even when offline. The criteria will evolve over time based on feedback from users and developers, but today they require sites to provide a
Web App Manifest
, serve all content using HTTPS, and at least partially work offline using a service worker.
ES6 Classes
Developers often find it hard to adapt to JavaScript’s prototype-based inheritance and although many libraries have introduced their own patterns for emulating classes, the language hasn't yet provided a single, uniform way of describing them.
ES6 classes
solve this by providing JavaScript a clean, standardized syntax for classes. This new syntax is available in Chrome 42 for JavaScript written in
strict mode
.
'use strict';
class Polygon {
constructor(height, width) {
this.name = 'Polygon';
this.height = height;
this.width = width;
}
sayName() {
log('Hi, I am a ', this.name + '.');
}
}
let p = new Polygon(300, 400);
Other updates in this release
DevTools now allows developers to
visually edit cubic beziers
directly from the styles pane, making it easier to understand and modify animations.
The Fetch API
is now available in the
window context
, shared workers, and
dedicated workers,
providing a new
promise
-based standard for AJAX requests.
The startRendering method of an
OfflineAudioContext
instance
now returns a promise
that resolves when the audio has finished rendering, making it easier to design web apps that work with the
Web Audio API
.
AudioBufferSourceNode.buffer
can no longer be set more than once, protecting developers from the lack of control over when the new source starts.
Chrome OS now supports
screen.orientation
and fires the
DeviceOrientationEvent
when the device’s orientation changes significantly, allowing orientation-aware websites to operate correctly on Chrome OS devices.
This release includes an updated and unprefixed implementation of
Encrypted Media Extensions
, which allows media sites to discover and interact with digital rights management systems..
A
new content setting
allows users to automatically pause non-primary plugin content to save power.
Developers can turn it on to test how it interacts with their content
.
As always, visit
chromestatus.com/features
for a complete overview of Chrome’s developer features, and circle
+Google Chrome Developers
for more frequent updates.
Freezing Chrome for Ice Cream Sandwich
2015年3月3日火曜日
Posted by Aurimas Lutikas, Software Engineer
It seems like yesterday that Chrome was first introduced on mobile devices to users running Android 4.0 Ice Cream Sandwich (ICS). Since then, twenty-four new Chrome releases and three new Android versions (Jellybean, Kitkat and Lollipop) have shipped. We’ve worked hard to make sure each version was faster, simpler and more secure than the last.
In the last year, we’ve seen the number of Chrome users running ICS drop by thirty percent. Developing new features on older phones has become increasingly challenging, and supporting ICS takes time away from building new experiences on the devices owned by the vast majority of our users. So, with Chrome’s 42nd release, we’ll stop updating Chrome on ICS devices. After Chrome 42, users on ICS devices can continue to use Chrome but won’t get further updates.
We’re excited to sharpen our focus on moving the web forward. If you’re interested in learning more about this change, please see the
FAQ's
.
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