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Today we are releasing React 16.9. It contains several new features, bugfixes, and new deprecation warnings to help prepare for a future major release.

New Deprecations

Renaming Unsafe Lifecycle Methods

Over a year ago, we announced that unsafe lifecycle methods are getting renamed:

• componentWillMount → UNSAFE_componentWillMount
• componentWillReceiveProps → UNSAFE_componentWillReceiveProps
• componentWillUpdate → UNSAFE_componentWillUpdate

React 16.9 does not contain breaking changes, and the old names continue to work in this release. But you will now see a warning when using any of the old names:

As the warning suggests, there are usually better approaches for each of the unsafe methods. However, maybe you don’t have the time to migrate or test these components. In that case, we recommend running a “codemod” script that renames them automatically:

cd your_project
npx react-codemod rename-unsafe-lifecycles

(Note that it says npx, not npm. npx is a utility that comes with Node 6+ by default.)

Running this codemod will replace the old names like componentWillMount with the new names like UNSAFE_componentWillMount:

The new names like UNSAFE_componentWillMount will keep working in both React 16.9 and in React 17.x. However, the new UNSAFE_ prefix will help components with problematic patterns stand out during the code review and debugging sessions. (If you’d like, you can further discourage their use inside your app with the opt-in Strict Mode.)

Note

Learn more about our versioning policy and commitment to stability.

Deprecating javascript: URLs

URLs starting with javascript: are a dangerous attack surface because it’s easy to accidentally include unsanitized output in a tag like <a href> and create a security hole:

const userProfile = {
  website: "javascript: alert('you got hacked')",
};
// This will now warn:
<a href={userProfile.website}>Profile</a>

In React 16.9, this pattern continues to work, but it will log a warning. If you use javascript: URLs for logic, try to use React event handlers instead. (As a last resort, you can circumvent the protection with dangerouslySetInnerHTML, but it is highly discouraged and often leads to security holes.)

In a future major release, React will throw an error if it encounters a javascript: URL.

Deprecating “Factory” Components

Before compiling JavaScript classes with Babel became popular, React had support for a “factory” component that returns an object with a render method:

function FactoryComponent() {
  return { render() { return <div />; } }
}

This pattern is confusing because it looks too much like a function component — but it isn’t one. (A function component would just return the <div /> in the above example.)

This pattern was almost never used in the wild, and supporting it causes React to be slightly larger and slower than necessary. So we are deprecating this pattern in 16.9 and logging a warning if it’s encountered. If you rely on it, adding FactoryComponent.prototype = React.Component.prototype can serve as a workaround. Alternatively, you can convert it to either a class or a function component.

We don’t expect most codebases to be affected by this.

New Features

Async act() for Testing

React 16.8 introduced a new testing utility called act() to help you write tests that better match the browser behavior. For example, multiple state updates inside a single act() get batched. This matches how React already works when handling real browser events, and helps prepare your components for the future in which React will batch updates more often.

However, in 16.8 act() only supported synchronous functions. Sometimes, you might have seen a warning like this in a test but could not easily fix it:

An update to SomeComponent inside a test was not wrapped in act(...).

In React 16.9, act() also accepts asynchronous functions, and you can await its call:

await act(async () => {
  // ...
});

This solves the remaining cases where you couldn’t use act() before, such as when the state update was inside an asynchronous function. As a result, you should be able to fix all the remaining act() warnings in your tests now.

We’ve heard there wasn’t enough information about how to write tests with act(). The new Testing Recipes guide describes common scenarios, and how act() can help you write good tests. These examples use vanilla DOM APIs, but you can also use React Testing Library to reduce the boilerplate code. Many of its methods already use act() internally.

Please let us know on the issue tracker if you bump into any other scenarios where act() doesn’t work well for you, and we’ll try to help.

Performance Measurements with <React.Profiler>

In React 16.5, we introduced a new React Profiler for DevTools that helps find performance bottlenecks in your application. In React 16.9, we are also adding a programmatic way to gather measurements called <React.Profiler>. We expect that most smaller apps won’t use it, but it can be handy to track performance regressions over time in larger apps.

The <Profiler> measures how often a React application renders and what the “cost” of rendering is. Its purpose is to help identify parts of an application that are slow and may benefit from optimizations such as memoization.

A <Profiler> can be added anywhere in a React tree to measure the cost of rendering that part of the tree. It requires two props: an id (string) and an onRender callback (function) which React calls any time a component within the tree “commits” an update.

render(
  <Profiler id="application" onRender={onRenderCallback}>    <App>
      <Navigation {...props} />
      <Main {...props} />
    </App>
  </Profiler>);

To learn more about the Profiler and the parameters passed to the onRender callback, check out the Profiler docs.

Note:

Profiling adds some additional overhead, so it is disabled in the production build.

To opt into production profiling, React provides a special production build with profiling enabled. Read more about how to use this build at fb.me/react-profiling.

Notable Bugfixes

This release contains a few other notable improvements:

• A crash when calling findDOMNode() inside a <Suspense> tree has been fixed.
• A memory leak caused by retaining deleted subtrees has been fixed too.
• An infinite loop caused by setState in useEffect now logs an error. (This is similar to the error you see when you call setState in componentDidUpdate in a class.)

We’re thankful to all the contributors who helped surface and fix these and other issues. You can find the full changelog below.

An Update to the Roadmap

In November 2018, we have posted this roadmap for the 16.x releases:

• A minor 16.x release with React Hooks (past estimate: Q1 2019)
• A minor 16.x release with Concurrent Mode (past estimate: Q2 2019)
• A minor 16.x release with Suspense for Data Fetching (past estimate: mid 2019)

These estimates were too optimistic, and we’ve needed to adjust them.

tldr: We shipped Hooks on time, but we’re regrouping Concurrent Mode and Suspense for Data Fetching into a single release that we intend to release later this year.

In February, we shipped a stable 16.8 release including React Hooks, with React Native support coming a month later. However, we underestimated the follow-up work for this release, including the lint rules, developer tools, examples, and more documentation. This shifted the timeline by a few months.

Now that React Hooks are rolled out, the work on Concurrent Mode and Suspense for Data Fetching is in full swing. The new Facebook website that’s currently in active development is built on top of these features. Testing them with real code helped discover and address many issues before they can affect the open source users. Some of these fixes involved an internal redesign of these features, which has also caused the timeline to slip.

With this new understanding, here’s what we plan to do next.

One Release Instead of Two

Concurrent Mode and Suspense power the new Facebook website that’s in active development, so we are confident that they’re close to a stable state technically. We also now better understand the concrete steps before they are ready for open source adoption.

Originally we thought we would split Concurrent Mode and Suspense for Data Fetching into two releases. We’ve found that this sequencing is confusing to explain because these features are more related than we thought at first. So we plan to release support for both Concurrent Mode and Suspense for Data Fetching in a single combined release instead.

We don’t want to overpromise the release date again. Given that we rely on both of them in production code, we expect to provide a 16.x release with opt-in support for them this year.

An Update on Data Fetching

While React is not opinionated about how you fetch data, the first release of Suspense for Data Fetching will likely focus on integrating with opinionated data fetching libraries. For example, at Facebook we are using upcoming Relay APIs that integrate with Suspense. We will document how other opinionated libraries like Apollo can support a similar integration.

In the first release, we don’t intend to focus on the ad-hoc “fire an HTTP request” solution we used in earlier demos (also known as “React Cache”). However, we expect that both we and the React community will be exploring that space in the months after the initial release.

An Update on Server Rendering

We have started the work on the new Suspense-capable server renderer, but we don’t expect it to be ready for the initial release of Concurrent Mode. This release will, however, provide a temporary solution that lets the existing server renderer emit HTML for Suspense fallbacks immediately, and then render their real content on the client. This is the solution we are currently using at Facebook ourselves until the streaming renderer is ready.

Why Is It Taking So Long?

We’ve shipped the individual pieces leading up to Concurrent Mode as they became stable, including new context API, lazy loading with Suspense, and Hooks. We are also eager to release the other missing parts, but trying them at scale is an important part of the process. The honest answer is that it just took more work than we expected when we started. As always, we appreciate your questions and feedback on Twitter and in our issue tracker.

Installation

React

React v16.9.0 is available on the npm registry.

To install React 16 with Yarn, run:

yarn add react@^16.9.0 react-dom@^16.9.0

To install React 16 with npm, run:

npm install --save react@^16.9.0 react-dom@^16.9.0

We also provide UMD builds of React via a CDN:

<script crossorigin src="https://unpkg.com/react@16/umd/react.production.min.js"></script>
<script crossorigin src="https://unpkg.com/react-dom@16/umd/react-dom.production.min.js"></script>

Refer to the documentation for detailed installation instructions.

Changelog

React

• Add <React.Profiler> API for gathering performance measurements programmatically. (@bvaughn in #15172)
• Remove unstable_ConcurrentMode in favor of unstable_createRoot. (@acdlite in #15532)

React DOM

• Deprecate old names for the UNSAFE_* lifecycle methods. (@bvaughn in #15186 and @threepointone in #16103)
• Deprecate javascript: URLs as a common attack surface. (@sebmarkbage in #15047)
• Deprecate uncommon “module pattern” (factory) components. (@sebmarkbage in #15145)
• Add support for the disablePictureInPicture attribute on <video>. (@eek in #15334)
• Add support for onLoad event for <embed>. (@cherniavskii in #15614)
• Add support for editing useState state from DevTools. (@bvaughn in #14906)
• Add support for toggling Suspense from DevTools. (@gaearon in #15232)
• Warn when setState is called from useEffect, creating a loop. (@gaearon in #15180)
• Fix a memory leak. (@paulshen in #16115)
• Fix a crash inside findDOMNode for components wrapped in <Suspense>. (@acdlite in #15312)
• Fix pending effects from being flushed too late. (@acdlite in #15650)
• Fix incorrect argument order in a warning message. (@brickspert in #15345)
• Fix hiding Suspense fallback nodes when there is an !important style. (@acdlite in #15861 and #15882)
• Slightly improve hydration performance. (@bmeurer in #15998)

React DOM Server

• Fix incorrect output for camelCase custom CSS property names. (@bedakb in #16167)

React Test Utilities and Test Renderer

• Add act(async () => ...) for testing asynchronous state updates. (@threepointone in #14853)
• Add support for nesting act from different renderers. (@threepointone in #16039 and #16042)
• Warn in Strict Mode if effects are scheduled outside an act() call. (@threepointone in #15763 and #16041)
• Warn when using act from the wrong renderer. (@threepointone in #15756)

We are excited to announce a new release of the React Developer Tools, available today in Chrome, Firefox, and (Chromium) Edge!

What’s changed?

A lot has changed in version 4! At a high level, this new version should offer significant performance gains and an improved navigation experience. It also offers full support for React Hooks, including inspecting nested objects.

Visit the interactive tutorial to try out the new version or see the changelog for demo videos and more details.

Which versions of React are supported?

react-dom

• 0-14.x: Not supported
• 15.x: Supported (except for the new component filters feature)
• 16.x: Supported

react-native

• 0-0.61: Not supported
• 0.62: Will be supported (when 0.62 is released)

How do I get the new DevTools?

React DevTools is available as an extension for Chrome and Firefox. If you have already installed the extension, it should update automatically within the next couple of hours.

If you use the standalone shell (e.g. in React Native or Safari), you can install the new version from NPM:

npm install -g react-devtools@^4

Where did all of the DOM elements go?

The new DevTools provides a way to filter components from the tree to make it easier to navigate deeply nested hierarchies. Host nodes (e.g. HTML <div>, React Native <View>) are hidden by default, but this filter can be disabled:

How do I get the old version back?

If you are working with React Native version 60 (or older) you can install the previous release of DevTools from NPM:

npm install --dev react-devtools@^3

For older versions of React DOM (v0.14 or earlier) you will need to build the extension from source:

# Checkout the extension source
git clone https://github.com/facebook/react-devtools

cd react-devtools

# Checkout the previous release branch
git checkout v3

# Install dependencies and build the unpacked extension
yarn install
yarn build:extension

# Follow the on-screen instructions to complete installation

Thank you!

We’d like to thank everyone who tested the early release of DevTools version 4. Your feedback helped improve this initial release significantly.

We still have many exciting features planned and feedback is always welcome! Please feel free to open a GitHub issue or tag @reactjs on Twitter.

Today we are releasing React 16.13.0. It contains bugfixes and new deprecation warnings to help prepare for a future major release.

New Warnings

Warnings for some updates during render

A React component should not cause side effects in other components during rendering.

It is supported to call setState during render, but only for the same component. If you call setState during a render on a different component, you will now see a warning:

Warning: Cannot update a component from inside the function body of a different component.

This warning will help you find application bugs caused by unintentional state changes. In the rare case that you intentionally want to change the state of another component as a result of rendering, you can wrap the setState call into useEffect.

Warnings for conflicting style rules

When dynamically applying a style that contains longhand and shorthand versions of CSS properties, particular combinations of updates can cause inconsistent styling. For example:

<div style={toggle ? 
  { background: 'blue', backgroundColor: 'red' } : 
  { backgroundColor: 'red' }
}>
  ...
</div> 

You might expect this <div> to always have a red background, no matter the value of toggle. However, on alternating the value of toggle between true and false, the background color start as red, then alternates between transparent and blue, as you can see in this demo.

React now detects conflicting style rules and logs a warning. To fix the issue, don’t mix shorthand and longhand versions of the same CSS property in the style prop.

Warnings for some deprecated string refs

String Refs is an old legacy API which is discouraged and is going to be deprecated in the future:

<Button ref="myRef" />

(Don’t confuse String Refs with refs in general, which remain fully supported.)

In the future, we will provide an automated script (a “codemod”) to migrate away from String Refs. However, some rare cases can’t be migrated automatically. This release adds a new warning only for those cases in advance of the deprecation.

For example, it will fire if you use String Refs together with the Render Prop pattern:

class ClassWithRenderProp extends React.Component {
  componentDidMount() {
    doSomething(this.refs.myRef);
  }
  render() {
    return this.props.children();
  }
}

class ClassParent extends React.Component {
  render() {
    return (
      <ClassWithRenderProp>
        {() => <Button ref="myRef" />}
      </ClassWithRenderProp>
    );
  }
}

Code like this often indicates bugs. (You might expect the ref to be available on ClassParent, but instead it gets placed on ClassWithRenderProp).

You most likely don’t have code like this. If you do and it is intentional, convert it to React.createRef() instead:

class ClassWithRenderProp extends React.Component {
  myRef = React.createRef();
  componentDidMount() {
    doSomething(this.myRef.current);
  }
  render() {
    return this.props.children(this.myRef);
  }
}

class ClassParent extends React.Component {
  render() {
    return (
      <ClassWithRenderProp>
        {myRef => <Button ref={myRef} />}
      </ClassWithRenderProp>
    );
  }
}

Note

To see this warning, you need to have the babel-plugin-transform-react-jsx-self installed in your Babel plugins. It must only be enabled in development mode.

If you use Create React App or have the “react” preset with Babel 7+, you already have this plugin installed by default.

Deprecating React.createFactory

React.createFactory is a legacy helper for creating React elements. This release adds a deprecation warning to the method. It will be removed in a future major version.

Replace usages of React.createFactory with regular JSX. Alternately, you can copy and paste this one-line helper or publish it as a library:

let createFactory = type => React.createElement.bind(null, type);

It does exactly the same thing.

Deprecating ReactDOM.unstable_createPortal in favor of ReactDOM.createPortal

When React 16 was released, createPortal became an officially supported API.

However, we kept unstable_createPortal as a supported alias to keep the few libraries that adopted it working. We are now deprecating the unstable alias. Use createPortal directly instead of unstable_createPortal. It has exactly the same signature.

Other Improvements

Component stacks in hydration warnings

React adds component stacks to its development warnings, enabling developers to isolate bugs and debug their programs. This release adds component stacks to a number of development warnings that didn’t previously have them. As an example, consider this hydration warning from the previous versions:

While it’s pointing out an error with the code, it’s not clear where the error exists, and what to do next. This release adds a component stack to this warning, which makes it look like this:

This makes it clear where the problem is, and lets you locate and fix the bug faster.

Notable bugfixes

This release contains a few other notable improvements:

• In Strict Development Mode, React calls lifecycle methods twice to flush out any possible unwanted side effects. This release adds that behaviour to shouldComponentUpdate. This shouldn’t affect most code, unless you have side effects in shouldComponentUpdate. To fix this, move the code with side effects into componentDidUpdate.
• In Strict Development Mode, the warnings for usage of the legacy context API didn’t include the stack for the component that triggered the warning. This release adds the missing stack to the warning.
• onMouseEnter now doesn’t trigger on disabled <button> elements.
• ReactDOM was missing a version export since we published v16. This release adds it back. We don’t recommend using it in your application logic, but it’s useful when debugging issues with mismatching / multiple versions of ReactDOM on the same page.

We’re thankful to all the contributors who helped surface and fix these and other issues. You can find the full changelog below.

Installation

React

React v16.13.0 is available on the npm registry.

To install React 16 with Yarn, run:

yarn add react@^16.13.0 react-dom@^16.13.0

To install React 16 with npm, run:

npm install --save react@^16.13.0 react-dom@^16.13.0

We also provide UMD builds of React via a CDN:

<script crossorigin src="https://unpkg.com/react@16/umd/react.production.min.js"></script>
<script crossorigin src="https://unpkg.com/react-dom@16/umd/react-dom.production.min.js"></script>

Refer to the documentation for detailed installation instructions.

Changelog

React

• Warn when a string ref is used in a manner that’s not amenable to a future codemod (@lunaruan in #17864)
• Deprecate React.createFactory() (@trueadm in #17878)

React DOM

• Warn when changes in style may cause an unexpected collision (@sophiebits in #14181, #18002)
• Warn when a function component is updated during another component’s render phase (@acdlite in #17099)
• Deprecate unstable_createPortal (@trueadm in #17880)
• Fix onMouseEnter being fired on disabled buttons (@AlfredoGJ in #17675)
• Call shouldComponentUpdate twice when developing in StrictMode (@bvaughn in #17942)
• Add version property to ReactDOM (@ealush in #15780)
• Don’t call toString() of dangerouslySetInnerHTML (@sebmarkbage in #17773)
• Show component stacks in more warnings (@gaearon in #17922, #17586)

Concurrent Mode (Experimental)

• Warn for problematic usages of ReactDOM.createRoot() (@trueadm in #17937)
• Remove ReactDOM.createRoot() callback params and added warnings on usage (@bvaughn in #17916)
• Don’t group Idle/Offscreen work with other work (@sebmarkbage in #17456)
• Adjust SuspenseList CPU bound heuristic (@sebmarkbage in #17455)
• Add missing event plugin priorities (@trueadm in #17914)
• Fix isPending only being true when transitioning from inside an input event (@acdlite in #17382)
• Fix React.memo components dropping updates when interrupted by a higher priority update (@acdlite in #18091)
• Don’t warn when suspending at the wrong priority (@gaearon in #17971)
• Fix a bug with rebasing updates (@acdlite and @sebmarkbage in #17560, #17510, #17483, #17480)

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