Chrome 77 Beta: New performance metrics, new form capabilities, capabilities in origin trials and more

August 9th, 2019

Unless otherwise noted, changes described below apply to the newest Chrome beta channel release for Android, Chrome OS, Linux, macOS, and Windows. Learn more about the features listed here through the provided links or from the list on Chrome 77 is beta as of August 8, 2019.

New Performance Metrics

Largest Contentful Paint

It has not always been easy for developers to measure how quickly the main content of a web page loads and is visible to users. The usefulness of existing metrics varies. Some metrics are only measurable in a lab, while others tell nothing about content that users care about. Consider the example below, taken from a DevTools performance audit. At the time of the first contentful paint, there’s no content on screen that a user can interact with.

Largest Contentful Paint attempts to provide more meaningful data by using the largest content element as a proxy for when the main content of the page is likely visible to users.

You’re probably asking questions like what does the new metric track? When is the metric reported? How do I improve it if it’s slow? For answers to these and other questions, see “Largest Contentful Paint” on

First Input Timing

The PerformanceEventTiming interface provides timing information about the latency of the first discrete user interaction, specifically one of key down, mouse down, click, or the combination of pointer down and pointer up. Pointer down may be the start of scrolling, which is not tracked. This is a subset of the EventTiming API, but will be exposed in advance because it provides key metrics to help measure and optimize responsiveness.

New Form Capabilities

Many websites use custom form controls to either add features that aren’t available in standard controls or to tailor a form’s design. A drawback of custom controls is that data must be stored in hidden <input> elements.

Two new features support custom form controls. The formdata event lets sites use JavaScript instead of hidden <input> elements to add data to a form. With this feature, site builders add a formdata event listener to a form element. The passed event includes a FormData object containing the data being submitted, which can now be modified.

The formdata event only lets sites interact with the submission process. Form-associated custom elements let site creators build custom elements that act like built-in form controls, providing capabilities such as enabling input validation or submitting data to the server.

To learn more and to see example code, read More capable form controls on

Origin Trials

This version of Chrome introduces the origin trials listed below. Origin trials allow you to try new features and give feedback on usability, practicality, and effectiveness to the web standards community. To register for any of the origin trials currently supported in Chrome, including the ones listed below, visit the Origin Trials dashboard. To learn more about origin trials themselves, visit the Origin Trials Guide for Web Developers.

A Contact Picker for the Web

The Contact Picker API is a new, on-demand picker that allows users to select entries from their contact list and share limited details of the selected entries with a website. It allows users to share only what they want, when they want, and makes it easier for users to reach and connect with their friends and family. See A Contact Picker for the Web for details.

Other features in this release

Enter Key Hint

The enterkeyhint content attribute
is an enumerated attribute for <form> elements that specifies what action label (or icon) to present as the enter key on virtual keyboards. This allows authors to customize the presentation of the enter key to make it more helpful for users. The attribute takes one of enter, done, go, next, previous, search, or send.

Feature Policy Control over Document.domain

The document-domain policy governs access to document.domain. It is enabled by default, and, if disabled, attempting to set document.domain will throw an error.

Layout Instability Monitoring

Adds the LayoutShift interface
to the Performance API, allowing developers to monitor changes to a DOM element’s on-screen position.

Limit the “referer” Header’s Length to 4kB

Strips the referer header down to an origin when it’s size exceeds 4kB.
Servers will often behave in unexpected ways when presented with an overly-long referer header. This is unfortunate, because referer is one header whose length attackers generally retain control over when generating no-cors requests.

Limit registerProtocolHandler() url Argument to http/https

The registerProtocolHandler() now only accepts URLs with http or https schemas. Because the intent of the API is to allow an endpoint to handle something like an SMS message, for example, it doesn’t make much sense for handlers to be data URLs, blob URLs, and so on.

New Features for Intl.NumberFormat

This change improves Intl.NumberFormat by adding support for measurement units, currency and sign display policies, and scientific and compact notation.

Overscroll Behavior Logical Longhands

Adds CSS flow-relative properties for controlling overscroll behavior through logical dimensions. flow-relative properties are those that are interpreted relative to the flow of content. The new properties are overscroll-behavior-inline and overscroll-behavior-block.

PerformanceObserverInit Buffered Flag

Adds a buffered flag to observer.observe() so that PerformanceObserver can receive entries created before the call is executed.


Adds the incecandidateerror event which provides detailed information about WebRTC ICE candidate gathering failures, including the ones defined by STUN (RFC5389) and TURN (RFC5766).

Diagnosing ICE connectivity issues without access to detailed gathering failures can be a challenge. Support for ICE candidate errors is targeted towards better connectivity troubleshooting and network diagnostics.

Adds a method for triggering an ICE restart which causes a WebRTC connection to try to reconnect. This feature is already available in Chrome by passing the iceRestart argument to createOffer(). restartIce() is a version of this method that works regardless of signalingState.

Service Workers

Preserve Request Priorities through Service Worker
Preserves a request’s original priority when it passes through a service worker. Previously, all requests going through a service worker would get “High” priority. This means render-blocking style sheets would have their priority clamped, while less important resources would get boosted.

Service Workers Support Basic HTTP Authentication
Displays HTTP authentication dialog boxes even if the request was from a service worker. This shows the native login dialog shown when an HTTP 401 response is received.

Stop Action for Media Sessions

Adds stop as a MediaSessionAction for calls to MediaSession.setActionHandler(). An action is an event tied specifically to a common media function such as pause or play. The stop action handler is called when the site should stop the playback and clear the state if appropriate. Samples are available on GitHub.

Web Payments: Throw a TypeError on Invalid “basic-card” Data

The PaymentRequest constructor now throws a TypeError when invalid supportedNetworks or supportedTypes are specified for basic card payment.

See Deprecations and Removals for an additional Web Payments update item. For more about recent web payments updates, see W3C Payment API changes in Chrome 77.

Interoperability Improvements

Support Step Timing Functions jump-start|end|both|none

Adds support for a richer set of step animations. Firefox already supports jump-* step timing functions. The step timing functions jump-both, jump-none, jump-start and jump-end were introduced to the spec for easing functions in 2018. Two of these, jump-start and jump-end are aliases for start and end. The remaining two provide increased flexibility for step transitions by enabling step functions in which both or neither endpoint has a discontinuous step. Previously, one and only one of the two endpoints could have a step discontinuity. Adding support in Chromium improves cross-browser interoperability.

white-space: break-spaces

Adds the break-spaces value for the white-space property which specifies that any sequence of preserved white space that would otherwise overflow a line and hang (as per the CSS Text Module spec’s Trimming and Positioning rules) must be broken.

With white-space: pre-wrap it’s possible to wrap and preserve white space sequences in the middle of a text line. However, if there is a sequence at the end of the line, it either collapses or hangs, maybe overflowing its box area. The new value overflow-wrap: break-spaces allows authors to wrap and preserve these white space sequences. This can be also useful for textarea or contenteditable elements, so that white space sequences added by spacebar press events are handled properly and generate line breaks if needed. Finally, there is an ongoing effort to enhance interoperability of the line breaking CSS properties (white-space, word-break and overflow-wrap) and this new value was defined precisely to achieve that.

Deprecations, and Removals

Card Issuer Networks as Payment Method Names

Remotes support for calling PaymentRequest with card issuer networks (e.g., “visa”, “amex”, “mastercard”) in the supportedMethods field.

Deprecate Web MIDI Use on Insecure Origins

Web MIDI use is classified into two groups: non-privilege use, and privilege use with sysex permission. Until Chrome 77, only the latter use prompts users for permission. To reduce security concerns, permissions will always be requested regardless of sysex use. This means that using Web MIDI on insecure origins will no longer be allowed.

Deprecate WebVR 1.1 API

This API is now deprecated in Chrome, being replaced by the WebXR Device API, which is expected to ship in Chrome 78. The WebVR Origin Trial ended on July 24, 2018.

WebVR was never enabled by default in Chrome, and was never ratified as a web standard. The WebXR Device API is the replacement API for WebVR. Removing WebVR from Chrome allows us to focus on the future of WebXR and remove the maintenance burden of WebVR, as well as reaffirm that Chrome is committed to WebXR as the future for building immersive web-based experiences. Removal is expected in Chrome 79.