A declarative, efficient, and flexible JavaScript library for building user interfaces. reactjs.org
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Sebastian Markbåge a5297ece62
Don't flush synchronous work if we're in the middle of a ViewTransition async sequence (#32760)
Starting a View Transition is an async sequence. Since React can get a
sync update in the middle of sequence we sometimes interrupt that
sequence.

Currently, we don't actually cancel the View Transition so it can just
run as a partial. This ensures that we fully skip it when that happens,
as well as warn.

However, it's very easy to trigger this with just a setState in
useLayoutEffect right now. Therefore if we're inside the preparing
sequence of a startViewTransition, this delays work that would've
normally flushed in a microtask. ~Maybe we want to do the same for
Default work already scheduled through a scheduler Task.~ Edit: This was
already done.

`flushSync` currently will still lead to an interrupted View Transition
(with a warning). There's a tradeoff here whether we want to try our
best to preserve the guarantees of `flushSync` or favor the animation.
It's already possible to suspend at the root with `flushSync` which
means it's not always 100% guaranteed to commit anyway. We could treat
it as suspended. But let's see how much this is a problem in practice.
2025-03-26 14:40:23 -04:00
.codesandbox Codesandbox: upgrade to Node.js 18 (#26330) 2023-03-06 15:38:03 -05:00
.github [ci] Skip yarn install on cache hit (#32757) 2025-03-26 13:13:39 -04:00
compiler [compiler][be] Playground now uses tsup bundled plugin (#32759) 2025-03-26 14:31:20 -04:00
fixtures Don't flush synchronous work if we're in the middle of a ViewTransition async sequence (#32760) 2025-03-26 14:40:23 -04:00
packages Don't flush synchronous work if we're in the middle of a ViewTransition async sequence (#32760) 2025-03-26 14:40:23 -04:00
scripts Fix ownerStackLimit feature gating for tests (#32726) 2025-03-26 12:01:05 -04:00
.editorconfig Remove trim_trailing_whitespace from editorconfig (#31413) 2024-11-04 15:30:02 -05:00
.eslintignore Fix ESLint and Prettier configs for React Compiler (#29073) 2024-05-15 14:02:57 -07:00
.eslintrc.js Rerender useSwipeTransition when direction changes (#32379) 2025-02-20 18:13:09 -05:00
.git-blame-ignore-revs Add run prettier commit to .git-blame-ignore-revs 2024-07-18 17:42:45 -04:00
.gitattributes .gitattributes to ensure LF line endings when we should 2014-01-17 16:25:53 -08:00
.gitignore [forgive] Init (#31918) 2025-02-25 12:19:11 -05:00
.mailmap updates mailmap entries (#19824) 2020-09-12 13:05:52 -04:00
.nvmrc [ci] Standardize node version and timezones 2024-07-12 12:53:05 -04:00
.prettierignore [prettier] Ignore compiler/target (#31168) 2024-10-10 10:53:27 -04:00
.prettierrc.js [BE] switch to hermes parser for prettier (#30421) 2024-07-22 19:16:13 -04:00
.watchmanconfig .watchmanconfig must be valid json (#16118) 2019-07-11 19:01:02 -07:00
babel.config-react-compiler.js feat(eslint-plugin-react-hooks): merge rule from eslint-plugin-react-compiler into react-hooks plugin (#32416) 2025-03-12 21:43:06 -04:00
babel.config-ts.js Update babel configs used in jest (#32588) 2025-03-12 19:07:39 -04:00
babel.config.js Partially revert #32588 (#32621) 2025-03-15 15:21:57 -04:00
CHANGELOG-canary.md Add useActionState to CHANGELOG-canary.md (#28632) 2024-03-26 13:15:08 -04:00
CHANGELOG.md Fix headings in React 19 CHANGELOG (#31683) 2024-12-06 16:55:53 +01:00
CODE_OF_CONDUCT.md revert last grammatical edit (#25067) 2022-08-10 20:14:31 +01:00
CONTRIBUTING.md Fix: Updated link in CONTRIBUTING (#25381) 2022-10-03 10:29:57 -04:00
dangerfile.js Fix typo in dangerfile.js which results in an unreachable code path… (#32277) 2025-01-31 01:44:02 -05:00
LICENSE [Codemod] Update copyright header to Meta (#25315) 2022-10-18 11:19:24 -04:00
MAINTAINERS Update MAINTAINERS (#32238) 2025-01-27 13:40:45 -06:00
package.json Partially revert #32588 (#32621) 2025-03-15 15:21:57 -04:00
react.code-workspace created a vscode workspace file for the repo (#29830) 2024-06-13 16:23:42 +01:00
ReactVersions.js Fix canary version strings (#31721) 2024-12-12 14:11:24 -05:00
README.md [ez] Remove circleci badge from readme 2024-07-29 13:26:14 -04:00
SECURITY.md Create SECURITY.md (#15784) 2020-01-09 14:07:41 -08:00
yarn.lock feat(eslint-plugin-react-hooks): merge rule from eslint-plugin-react-compiler into react-hooks plugin (#32416) 2025-03-12 21:43:06 -04:00

React · GitHub license npm version (Runtime) Build and Test (Compiler) TypeScript PRs Welcome

React is a JavaScript library for building user interfaces.

  • Declarative: React makes it painless to create interactive UIs. Design simple views for each state in your application, and React will efficiently update and render just the right components when your data changes. Declarative views make your code more predictable, simpler to understand, and easier to debug.
  • Component-Based: Build encapsulated components that manage their own state, then compose them to make complex UIs. Since component logic is written in JavaScript instead of templates, you can easily pass rich data through your app and keep the state out of the DOM.
  • Learn Once, Write Anywhere: We don't make assumptions about the rest of your technology stack, so you can develop new features in React without rewriting existing code. React can also render on the server using Node and power mobile apps using React Native.

Learn how to use React in your project.

Installation

React has been designed for gradual adoption from the start, and you can use as little or as much React as you need:

Documentation

You can find the React documentation on the website.

Check out the Getting Started page for a quick overview.

The documentation is divided into several sections:

You can improve it by sending pull requests to this repository.

Examples

We have several examples on the website. Here is the first one to get you started:

import { createRoot } from 'react-dom/client';

function HelloMessage({ name }) {
  return <div>Hello {name}</div>;
}

const root = createRoot(document.getElementById('container'));
root.render(<HelloMessage name="Taylor" />);

This example will render "Hello Taylor" into a container on the page.

You'll notice that we used an HTML-like syntax; we call it JSX. JSX is not required to use React, but it makes code more readable, and writing it feels like writing HTML.

Contributing

The main purpose of this repository is to continue evolving React core, making it faster and easier to use. Development of React happens in the open on GitHub, and we are grateful to the community for contributing bugfixes and improvements. Read below to learn how you can take part in improving React.

Code of Conduct

Facebook has adopted a Code of Conduct that we expect project participants to adhere to. Please read the full text so that you can understand what actions will and will not be tolerated.

Contributing Guide

Read our contributing guide to learn about our development process, how to propose bugfixes and improvements, and how to build and test your changes to React.

Good First Issues

To help you get your feet wet and get you familiar with our contribution process, we have a list of good first issues that contain bugs that have a relatively limited scope. This is a great place to get started.

License

React is MIT licensed.