Andrew ClarkandGitHub
9fbb6dc69e
Implements Promise as a valid React node types. The idea is that any type that can be unwrapped with `use` should also be renderable. When the reconciler encounters a Usable in a child position, it will transparently unwrap the value before reconciling it. The value of the inner value will determine the identity of the child during reconciliation, not the Usable object that wraps around it. Unlike `use`, the reconciler will recursively unwrap the value until it reaches a non-Usable type, e.g. `Usable<Usable<Usable<T>>>` will resolve to T. In this initial commit, I've added support for Promises. I will do Context in the [next step](https://github.com/facebook/react/pull/25641). Being able to render a promise as a child has several interesting implications. The Server Components response format can use this feature in its implementation — instead of wrapping references to client components in `React.lazy`, it can just use a promise. This also fulfills one of the requirements for async components on the client, because an async component always returns a promise for a React node. However, we will likely warn and/or lint against this for the time being because there are major caveats if you re-render an async component in response to user input. (Note: async components already work in a Server Components environment — the caveats only apply to running them in the browser.) To suspend, React uses the same algorithm as `use`: by throwing an exception to unwind the stack, then replaying the begin phase once the promise resolves. It's a little weird to suspend during reconciliation, however, `lazy` already does this so if there were any obvious bugs related to that we likely would have already found them. Still, the structure is a bit unfortunate. Ideally, we shouldn't need to replay the entire begin phase of the parent fiber in order to reconcile the children again. This would require a somewhat significant refactor, because reconciliation happens deep within the begin phase, and depending on the type of work, not always at the end. We should consider as a future improvement.
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.