Andrew Clark
3a50d95573
I noticed a weird branch where we attach a ping listener even in legacy mode. It's weird because this shouldn't be necessary. Fallbacks always synchronously commit in legacy mode, so pings never happen. (A "ping" is when a suspended promise resolves before the fallback has committed.) It took me a moment to remember why this case exists, but it's related to React.lazy. There's a special case where we suspend while reconciling the children of a Suspense boundary's inner Offscreen wrapper fiber. This happens when a React.lazy component is a direct child of a Suspense boundary. Suspense boundaries are implemented as multiple fibers, but they are a single conceptual unit. The legacy mode behavior where we pretend the suspended fiber committed as `null` won't work, because in this case the "suspended" fiber is the inner Offscreen wrapper. Because the contents of the boundary haven't started rendering yet (i.e. nothing in the tree has partially rendered) we can switch to the regular, concurrent mode behavior: mark the boundary with ShouldCapture and enter the unwind phase. However, even though we're switching to the concurrent mode behavior, we don't need to attach a ping listener. So I refactored the logic so that it doesn't escape back into the regular path. It's not really a big deal that we attach an unncessary ping listener, since this case is so unusual. The motivation is not performance related — it's to make the logic clearer, because I'm about to add another case where we trigger a Suspense boundary without attaching a ping listener.
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:
function HelloMessage({ name }) {
return <div>Hello {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 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 which have a relatively limited scope. This is a great place to get started.
License
React is MIT licensed.