Chromium Blog
News and developments from the open source browser project
Chrome 63 Beta: Dynamic module imports, async iterators and generators, Device Memory API, and permissions UI changes
pátek 27. října 2017
Unless otherwise noted, changes described below apply to the newest Chrome
Beta
channel release for Android, Chrome OS, Linux, Mac, and Windows.
Dynamic module imports
Currently, importing JavaScript modules is completely static, and developers cannot import modules based on runtime conditions, like whether a user is logged in. Starting in this release, the
import(specifier)
syntax now allows developers to
dynamically load code
into modules and scripts at runtime. This can be used for lazy loading a script only when it’s needed, which improves performance of the application.
button.addEventListener('click', event => {
import('./dialogBox.js')
.then(dialogBox => {
dialogBox.open();
})
.catch(error => {
/* Error handling */
});
});
The
code example
above shows how to use the import(specifier) function to import JavaScript after an event
.
Async iterators and generators
Writing code that does any sort of iteration with async functions can be inelegant. The new
async generator functions
using the
async iteration
protocol
are now available to help developers streamline the consumption or implementation of streaming data sources. Async iterators can be used in
for
loops and also to create custom async iterators through async iterator factories.
async function* getChunkSizes(url) {
const response = await fetch(url);
for await (const chunk of streamAsyncIterator(response.body))
{
yield chunk.length;
}
}
The code example above shows how to use async iterators to writer cleaner code for streaming fetches, using the
streamAsyncIterator function
.
Device Memory API
It’s challenging for developers to create one user experience that can work across all devices, due to varying device capabilities. The new
Device Memory JavaScript API
helps developers with this challenge by using the total RAM on a user’s machine to provide insights into device constraints. This insight enables developers to tailor content at runtime in accordance with hardware limitations. For example, developers can serve a “lite” app to users on low-end devices, resulting in better experiences and fewer frustrations. The Device Memory API can also be used to add context to metrics, such as the amount of time a task takes to complete in JavaScript, through the lens of device memory.
Permissions UI changes
When websites need special permissions from a user, they trigger a permission request. Currently these permission requests appear in Chrome for Android as ignorable banners at the bottom of the screen, and developers often show them without considering whether the user has the appropriate context to grant the permission. This results in a distracting user experience, and users ignore or temporarily dismiss these permission prompts more than 90% of the time.
In Chrome 59, we started to address this problem by
temporarily blocking
a permission if the user dismisses the request three times. As a next step, in this release Chrome for Android now presents permission requests as modal dialogs. This change reduces the overall number of permission prompts by 50%. It also makes users 5 times more likely to accept or deny requests, rather than temporarily dismissing or repeatedly ignoring them. To ensure users understand the permission request, developers should present users with permission requests
at an appropriate time
, as we’ve found that users were 2.5 times more likely to grant permission to a site that ask for permissions with context.
Other features in this release
Blink > Bindings
To improve interoperability, a
TypeError
is now thrown for
EventTarget.addEventListener and removeEventListener
when the callback passed is not an
EventListener
,
null
, or
undefined
.
Blink > CSS
Developers can now
make pixel-level adjustments
using the new
Q
length
unit
, which is especially useful on small viewports.
Developers can now prevent apps from using Chrome’s pull-to-refresh feature or create custom effects using
overscroll-behavior
, which allows changing the browser’s behavior once the scroller has
reached
its full extent.
Blink > Fonts
font-variant-east-asian
is now supported, allowing developers to control the
usage of alternate glyphs
for East Asian languages like Japanese and Chinese.
Blink > HTML
To improve interoperability, Chrome will fire
beforeprint
and
afterprint
events as part of the
printing standard
, allowing developers to to annotate the printed copy and edit the annotation after the printing command is done executing.
Blink > JavaScript
Using
Promise.prototype.finally
, a callback can
now be registered
to be invoked after a Promise has been fulfilled or rejected.
The
Intl.PluralRules
API
allows developers to build applications that understand pluralization of a given language by indicating which plural form applies for a given number and language.
Blink > MediaStream
MediaStreamTrack.applyConstraints()
is now supported for local video
MediaStreamTracks
, including tracks obtained from
getUserMedia()
,
capture from media elements
or screen capture.
Blink > Network
Version 2
of
NT LAN Manager (NTLM) API
is now shipped, enabling applications to authenticate remote users and provide session security when requested by the application.
Blink > Sensor
Thanks to contributors from engineers at Intel,
an Origin Trial is now available
that exposes the following sensors via the new Generic Sensors API syntax: A
ccelerometer, LinearAccelerationSensor, Gyroscope, AbsoluteOrientationSensor
, and
RelativeOrientationSensor
.
Blink > Storage
The
localStorage
and
sessionStorage
API's now use
getItem()
rather than an anonymous getter, so attempting to access a key using
getItem()
will now return
null
rather than
undefined
. Thanks to Intel for the contribution!
To improve developer experience, the
methods on
sessionStorage
and
localStorage
such as
getItem()
,
removeItem()
, and
clear()
are now enumerable. Thanks to Intel for making this happen!
UI > Browser > Mobile (Android)
display: minimal-ui
is now supported by Chrome on Android, enabling developers to
display a UI similar to Chrome Custom Tabs
for users.
Deprecations and interoperability improvements
Blink > Bindings
To improve interoperability,
instance properties
with a Promise type now return a rejected promise instead of throwing an exception.
Blink > CSS
The
/deep/
or
>>>
, selector, as well as
::shadow,
are
now
removed
from CSS dynamic profile, following their
deprecation
in Chrome 45.
Blink > DOM
To improve interoperability,
HTMLAllCollection
,
HTMLCollection
,
HTMLFormControlsCollection
and
HTMLOptionsCollection
are no longer enumerable, so they are now left out of calls to
Object.keys()
or
for
-
in
loops.
Posted by
Sathya Gunasekaran, Lazily-Loaded Engineer
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