Sebastian Markbåge
fe21c947c8
This flag first moves the `shouldYield()` logic into React itself. We need this for `postTask` compatibility anyway since this logic is no longer a concern of the scheduler. This means that there can also be no global `requestPaint()` that asks for painting earlier. So this is best rolled out with `enableAlwaysYieldScheduler` (and ideally `enableYieldingBeforePassive`) instead of `enableRequestPaint`. Once in React we can change the yield timing heuristics. This uses the previous 5ms for Idle work to keep everything responsive while doing background work. However, for Transitions and Retries we have seen that same thread animations (like loading states animating, or constant animations like cool Three.js stuff) can take CPU time away from the Transition that causes moving into new content to slow down. Therefore we only yield every 25ms. The purpose of this yield is not to avoid the overhead of yielding, which is very low, but rather to intentionally block any frequently occurring other main thread work like animations from starving our work. If we could we could just tell everyone else to throttle their stuff for ideal scheduling but that's not quite realistic. In other words, the purpose of this is to reduce the frame rate of animations to 30 fps and we achieve this by not yielding. We still do yield to allow the animations to not just stall. This seems like a good balance. The 5ms of Idle is because we don't really need to yield less often since the overhead is low. We keep it low to allow 120 fps animations to run if necessary and our work may not be the only work within a frame so we need to yield early enough to leave enough time left. Similarly we choose 25ms rather than say 35ms to ensure that we push long enough to guarantee to half the frame rate but low enough that there's plenty of time left for a rAF to power each animation every other frame. It's also low enough that if something else interrupts the work like a new interaction, we can still be responsive to that within 50ms or so. We also need to yield in case there's I/O work that needs to get bounced through the main thread. This flag is currently off everywhere since we have so many other scheduling flags but that means there's some urgency to roll those out fully so we can test this one. There's also some tests to update since this doesn't go through the Mock scheduler anymore for yields.
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 Quick Start to get a taste of React.
- Add React to an Existing Project to use as little or as much React as you need.
- Create a New React App if you're looking for a powerful JavaScript toolchain.
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:
- Quick Start
- Tutorial
- Thinking in React
- Installation
- Describing the UI
- Adding Interactivity
- Managing State
- Advanced Guides
- API Reference
- Where to Get Support
- Contributing Guide
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.
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.