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Today if something suspends, React will continue rendering the siblings of that component. Our original rationale for prerendering the siblings of a suspended component was to initiate any lazy fetches that they might contain. This was when we were more bullish about lazy fetching being a good idea some of the time (when combined with prefetching), as opposed to our latest thinking, which is that it's almost always a bad idea. Another rationale for the original behavior was that the render was I/O bound, anyway, so we might as do some extra work in the meantime. But this was before we had the concept of instant loading states: when navigating to a new screen, it's better to show a loading state as soon as you can (often a skeleton UI), rather than delay the transition. (There are still cases where we block the render, when a suitable loading state is not available; it's just not _all_ cases where something suspends.) So the biggest issue with our existing implementation is that the prerendering of the siblings happens within the same render pass as the one that suspended — _before_ the loading state appears. What we should do instead is immediately unwind the stack as soon as something suspends, to unblock the loading state. If we want to preserve the ability to prerender the siblings, what we could do is schedule special render pass immediately after the fallback is displayed. This is likely what we'll do in the future. However, in the new implementation of `use`, there's another reason we don't prerender siblings: so we can preserve the state of the stack when something suspends, and resume where we left of when the promise resolves without replaying the parents. The only way to do this currently is to suspend the entire work loop. Fiber does not currently support rendering multiple siblings in "parallel". Once you move onto the next sibling, the stack of the previous sibling is discarded and cannot be restored. We do plan to implement this feature, but it will require a not-insignificant refactor. Given that lazy data fetching is already bad for performance, the best trade off for now seems to be to disable prerendering of siblings. This gives us the best performance characteristics when you're following best practices (i.e. hoist data fetches to Server Components or route loaders), at the expense of making an already bad pattern a bit worse. Later, when we implement resumable context stacks, we can reenable sibling prerendering. Though even then the use case will mostly be to prerender the CPU-bound work, not lazy fetches.
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.