New in Chrome 83

Chrome 83 is starting to roll out to stable now.

Here's what you need to know:

• Trusted types help prevent cross site scripting vulnerabilities.
• Form elements get an important make-over.
• There's a new way to detect memory leaks.
• The native file system API starts a new origin trial with added functionality.
• There are new cross-origin policies
• We've introduced the Web Vitals program, to provide unified guidance for quality signals that, we believe, are essential to delivering a great user experience on the web.
• And more.

I'm Pete LePage, working and shooting from home, let's dive in and see what's new for developers in Chrome 83!

# Trusted types

DOM-based cross-site scripting is one of the most common security vulnerabilities on the web. It can be easy to accidentally introduce one to your page. Trusted types can help prevent these kinds of vulnerabilities, because they require you to process the data before passing it into a potentially dangerous function.

Take innerHTML for example, with trusted types turned on, if I try to pass a string, it'll fail with a TypeError because the browser doesn't know if it can trust the string.

// Trusted types turned on
const elem = document.getElementById('myDiv');
elem.innerHTML = `Hello, world!`;
// Will throw a TypeError

Instead, I need to either use a safe function, like textContent, pass in a trusted type, or create the element and use appendChild().

// Use a safe function
elem.textContent = ''; // OK

// Pass in a trusted type
import DOMPurify from 'dompurify';
const str = `Hello, world!`;
elem.innerHTML = DOMPurify.sanitize(str, {RETURN_TRUSTED_TYPE: true});

// Create an element
const img = document.createElement('img');
img.src = 'xyz.jpg';
elem.appendChild(img);

Before you turn on trusted types, you'll want to identify and fix any violations using a report-only CSP header.

Content-Security-Policy-Report-Only: require-trusted-types-for 'script'; report-uri //example.com

Then once you've got everything buttoned up, you can turn it on properly. Complete details are in Prevent DOM-based cross-site scripting vulnerabilities with Trusted Types on web.dev.

# Updates to form controls

We use HTML form controls every day, and they are key to so much of the web's interactivity. They're easy to use, have built-in accessibility, and are familiar to our users. The styling of form controls can be inconsistent across browsers and operating systems. And we frequently have to ship a number of CSS rules just to get a consistent look across devices.

I've been really impressed by the work Microsoft has been doing to modernize the appearance of form controls. Beyond the nicer visual style, they bring better touch support, and better accessibility, including improved keyboard support!

The new form controls have already landed in Microsoft Edge, and are now available in Chrome 83. For more information, see Updates to Form Controls and Focus on the Chromium blog.

# Origin trials

# Measure memory with measureMemory()

Starting an origin trial in Chrome 83, performance.measureMemory() is a new API that makes it possible to measure the memory usage of your page, and detect memory leaks.

Memory leaks are easy to introduce:

• Forgetting to unregister an event listener
• Capturing objects from an iframe
• Not closing a worker
• Accumulating objects in arrays
• and so on.

Memory leaks lead to pages that appear slow, and bloated to users.

if (performance.measureMemory) {
  try {
    const result = await performance.measureMemory();
    console.log(result);
  } catch (err) {
    console.error(err);
  }
}

Check out Monitor your web page's total memory usage with measureMemory() on web.dev for all the details of the new API.

# Updates to the Native File System API

The Native File System API started a new origin trial in Chrome 83 with support for writable streams, and the ability to save file handles.

async function writeURLToFile(fileHandle, url) {
  // Create a FileSystemWritableFileStream to write to.
  const writable = await fileHandle.createWritable();
  // Make an HTTP request for the contents.
  const response = await fetch(url);
  // Stream the response into the file.
  await response.body.pipeTo(writable);
  // pipeTo() closes the destination pipe automatically.
}

Writable streams make it much easier to write to a file, and because it's a stream, you can easily pipe responses from one stream to another.

Saving file handles to IndexedDB allows you to store state, or remember which files a user was working on. For example keep a list of recently edited files, open the last file that the user was working on, and so on.

You'll need a new origin trial token to use these features, so check out my updated article The Native File System API: Simplifying access to local files on web.dev with all the details, and how to get your new origin trial token.

# Other origin trials

Check </origintrials/#/trials/active> for a complete list of features in origin trial.

# New cross-origin policies

Some web APIs increase the risk of side-channel attacks like Spectre. To mitigate that risk, browsers offer an opt-in-based isolated environment called cross-origin isolated. The cross-origin isolated state also prevents modifications of document.domain. Being able to alter document.domain allows communication between same-site documents and has been considered a loophole in the same-origin policy.

Check out Eiji's post Making your website "cross-origin isolated" using COOP and COEP for complete details.

# Web vitals

Measuring the quality of user experience has many facets. While some aspects of user experience are site and context specific, there is a common set of signals—"Core Web Vitals"—that is critical to all web experiences. Such core user experience needs include loading experience, interactivity, and visual stability of page content, and combined are the foundation of the 2020 Core Web Vitals.

• Largest Contentful Paint measures perceived load speed and marks the point in the page load timeline when the page's main content has likely loaded.
• First Input Delay measures responsiveness and quantifies the experience users feel when trying to first interact with the page.
• Cumulative Layout Shift measures visual stability and quantifies the amount of unexpected layout shift of visible page content.

All of these metrics capture important user-centric outcomes, are field measurable, and have supporting lab diagnostic metric equivalents and tooling. For example, while Largest Contentful Paint is the topline loading metric, it is also highly dependent on First Contentful Paint (FCP) and Time to First Byte (TTFB), which remain critical to monitor and improve.

To learn more, check out Introducing Web Vitals: essential metrics for a healthy site on the Chromium Blog for complete details.

# And more

• Chrome now supports the Barcode Detection API, which provides the ability to detect and decode barcodes.
• The new CSS @supports function provides feature detection for CSS selectors.
• New ARIA annotations support screen reader accessibility for comments, suggestions, and text highlights with semantic meanings (similar to <mark>).
• The prefers-color-scheme media query lets authors support their own dark theme so they have full control over experiences they build.
• JavaScript now supports modules in shared workers.

Curious about what's coming in the future? Check out the Fugu API Tracker to see!

# Further reading

This covers only some of the key highlights. Check the links below for additional changes in Chrome 83.

• What's new in Chrome DevTools (83)
• Chrome 83 deprecations & removals
• ChromeStatus.com updates for Chrome 83
• What's new in JavaScript in Chrome 83
• Chromium source repository change list

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I'm Pete LePage, and I need a hair cut, but as soon as Chrome 84 is released, I'll be right here to tell you -- what's new in Chrome!