cd2b79dedd
Implements initial (client-only) support for async actions behind a flag. This is an experimental feature and the design isn't completely finalized but we're getting closer. It will be layered alongside other features we're working on, so it may not feel complete when considered in isolation. The basic description is you can pass an async function to `startTransition` and all the transition updates that are scheduled inside that async function will be grouped together. The `isPending` flag will be set to true immediately, and only set back to false once the async action has completed (as well as all the updates that it triggers). The ideal behavior would be that all updates spawned by the async action are automatically inferred and grouped together; however, doing this properly requires the upcoming (stage 2) Async Context API, which is not yet implemented by browsers. In the meantime, we will fake this by grouping together all transition updates that occur until the async function has terminated. This can lead to overgrouping between unrelated actions, which is not wrong per se, just not ideal. If the `useTransition` hook is removed from the UI before an async action has completed — for example, if the user navigates to a new page — subsequent transitions will no longer be grouped with together with that action. Another consequence of the lack of Async Context is that if you call `setState` inside an action but after an `await`, it must be wrapped in `startTransition` in order to be grouped properly. If we didn't require this, then there would be no way to distinguish action updates from urgent updates caused by user input, too. This is an unfortunate footgun but we can likely detect the most common mistakes using a lint rule. Once Async Context lands in browsers, we can start warning in dev if we detect an update that hasn't been wrapped in `startTransition`. Then, longer term, once the feature is ubiquitous, we can rely on it for real and allow you to call `setState` without the additional wrapper. Things that are _not_ yet implemented in this PR, but will be added as follow ups: - Support for non-hook form of `startTransition` - Canceling the async action scope if the `useTransition` hook is deleted from the UI - Anything related to server actions
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 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:
- 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:
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. 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 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.