Andrew Clark
33226fadaa
* [useSyncExternalStore] Remove extra hook object Because we already track `getSnapshot` and `value` on the store instance, we don't need to also track them as effect dependencies. And because the effect doesn't require any clean-up, we don't need to track a `destroy` function. So, we don't need to store any additional state for this effect. We can call `pushEffect` directly, and only during renders where something has changed. This saves some memory, but my main motivation is because I plan to use this same logic to schedule a pre-commit consistency check. (See the inline comments for more details.) * Split shouldTimeSlice into two separate functions Lanes that are blocking (SyncLane, and DefaultLane inside a blocking- by-default root) are always blocking for a given root. Whereas expired lanes can expire while the render phase is already in progress. I want to check if a lane is blocking without checking whether it expired, so I split `shouldTimeSlice` into two separate functions. I'll use this in the next step. * Check for store mutations before commit When a store is read for the first time, or when `subscribe` or `getSnapshot` changes, during a concurrent render, we have to check at the end of the render phase whether the store was mutated by an concurrent event. In the userspace shim, we perform this check in a layout effect, and patch up any inconsistencies by scheduling another render + commit. However, even though we patch them up in the next render, the parent layout effects that fire in the original render will still observe an inconsistent tree. In the native implementation, we can instead check for inconsistencies right after the root is completed, before entering the commit phase. If we do detect a mutaiton, we can discard the tree and re-render before firing any effects. The re-render is synchronous to block further concurrent mutations (which is also what we do to recover from tearing bugs that result in an error). After the synchronous re-render, we can assume the tree the tree is consistent and continue with the normal algorithm for finishing a completed root (i.e. either suspend or commit). The result is that layout effects will always observe a consistent tree.
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.