* Don't warn if an unmounted component is pinged * Suspense fuzz tester The fuzzer works by generating a random tree of React elements. The tree two types of custom components: - A Text component suspends rendering on initial mount for a fuzzy duration of time. It may update a fuzzy number of times; each update supsends for a fuzzy duration of time. - A Container component wraps some children. It may remount its children a fuzzy number of times, by updating its key. The tree may also include nested Suspense components. After this tree is generated, the tester sets a flag to temporarily disable Text components from suspending. The tree is rendered synchronously. The output of this render is the expected output. Then the tester flips the flag back to enable suspending. It renders the tree again. This time the Text components will suspend for the amount of time configured by the props. The tester waits until everything has resolved. The resolved output is then compared to the expected output generated in the previous step. Finally, we render once more, but this time in concurrent mode. Once again, the resolved output is compared to the expected output. I tested by commenting out various parts of the Suspense implementation to see if broke in the expected way. I also confirmed that it would have caught #14133, a recent bug related to deletions. * When a generated test case fails, log its input * Moar fuzziness Adds more fuzziness to the generated tests. Specifcally, introduces nested Suspense cases, where the fallback of a Suspense component also suspends. This flushed out a bug (yay!) whose test case I've hard coded. * Use seeded random number generator So if there's a failure, we can bisect.
React ·

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 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 own 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:
- Use Online Playgrounds to get a taste of React.
- Add React to a Website as a
<script>tag in one minute. - Create a New React App if you're looking for a powerful JavaScript toolchain.
You can use React as a <script> tag from a CDN, or as a react package on npm.
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:
class HelloMessage extends React.Component {
render() {
return <div>Hello {this.props.name}</div>;
}
}
ReactDOM.render(
<HelloMessage name="Taylor" />,
document.getElementById('container')
);
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. If you're using React as a <script> tag, read this section on integrating JSX; otherwise, the recommended JavaScript toolchains handle it automatically.
Contributing
The main purpose of this repository is to continue to evolve 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 which have a relatively limited scope. This is a great place to get started.
License
React is MIT licensed.