Andrew ClarkandGitHub
6eaadc1019
* Yield to main thread if continuation is returned
Instead of using an imperative method `requestYield` to ask Scheduler to
yield to the main thread, we can assume that any time a Scheduler task
returns a continuation callback, it's because it wants to yield to the
main thread. We can assume the task already checked some condition that
caused it to return a continuation, so we don't need to do any
additional checks — we can immediately yield and schedule a new task
for the continuation.
The replaces the `requestYield` API that I added in 76da3fb.
* Move unwind after error into main work loop
I need to be able to yield to the main thread in between when an error
is thrown and when the stack is unwound. (This is the motivation behind
the refactor, but it isn't implemented in this commit.) Currently the
unwind is inlined directly into `handleError`.
Instead, I've moved the unwind logic into the main work loop. At the
very beginning of the function, we check to see if the work-in-progress
is in a "suspended" state — that is, whether it needs to be unwound. If
it is, we will enter the unwind phase instead of the begin phase.
We only need to perform this check when we first enter the work loop:
at the beginning of a Scheduler chunk, or after something throws. We
don't need to perform it after every unit of work.
* Yield to main thread whenever a fiber suspends
When a fiber suspends, we should yield to the main thread in case the
data is already cached, to unblock a potential ping event.
By itself, this commit isn't useful because we don't do anything special
in the case where to do receive an immediate ping event. I've split this
out only to demonstrate that it doesn't break any existing behavior.
See the next commit for full context and motivation.
* Resume immediately pinged fiber without unwinding
If a fiber suspends, and is pinged immediately in a microtask (or a
regular task that fires before React resumes rendering), try rendering
the same fiber again without unwinding the stack. This can be super
helpful when working with promises and async-await, because even if the
outermost promise hasn't been cached before, the underlying data may
have been preloaded. In many cases, we can continue rendering
immediately without having to show a fallback.
This optimization should work during any concurrent (time-sliced)
render. It doesn't work during discrete updates because those are
semantically required to finish synchronously — those get the current
behavior.
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 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.