Sebastian MarkbågeandGitHub
3bdc4aba5b
This adds an experimental `unstable_postpone(reason)` API. Currently we don't have a way to model effectively an Infinite Promise. I.e. something that suspends but never resolves. The reason this is useful is because you might have something else that unblocks it later. E.g. by updating in place later, or by client rendering. On the client this works to model as an Infinite Promise (in fact, that's what this implementation does). However, in Fizz and Flight that doesn't work because the stream needs to end at some point. We don't have any way of knowing that we're suspended on infinite promises. It's not enough to tag the promises because you could await those and thus creating new promises. The only way we really have to signal this through a series of indirections like async functions, is by throwing. It's not 100% safe because these values can be caught but it's the best we can do. Effectively `postpone(reason)` behaves like a built-in [Catch Boundary](https://github.com/facebook/react/pull/26854). It's like `raise(Postpone, reason)` except it's built-in so it needs to be able to be encoded and caught by Suspense boundaries. In Flight and Fizz these behave pretty much the same as errors. Flight just forwards it to retrigger on the client. In Fizz they just trigger client rendering which itself might just postpone again or fill in the value. The difference is how they get logged. In Flight and Fizz they log to `onPostpone(reason)` instead of `onError(error)`. This log is meant to help find deopts on the server like finding places where you fall back to client rendering. The reason that you pass in is for that purpose to help the reason for any deopts. I do track the stack trace in DEV but I don't currently expose it to `onPostpone`. This seems like a limitation. It might be better to expose the Postpone object which is an Error object but that's more of an implementation detail. I could also pass it as a second argument. On the client after hydration they don't get passed to `onRecoverableError`. There's no global `onPostpone` API to capture postponed things on the client just like there's no `onError`. At that point it's just assumed to be intentional. It doesn't have any `digest` or reason passed to the client since it's not logged. There are some hacky solutions that currently just tries to reuse as much of the existing code as possible but should be more properly implemented. - Fiber is currently just converting it to a fake Promise object so that it behaves like an infinite Promise. - Fizz is encoding the magic digest string `"POSTPONE"` in the HTML so we know to ignore it but it should probably just be something neater that doesn't share namespace with digests. Next I plan on using this in the `/static` entry points for additional features. Why "postpone"? It's basically a synonym to "defer" but we plan on using "defer" for other purposes and it's overloaded anyway.
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.