Andrew ClarkandGitHub
c820097716
Certain fiber types may have a ref attached to them. The main ones are HostComponent and ClassComponent. During the render phase, we check if a ref was passed to it, and if so, we schedule a Ref effect: `markRef`. Currently, we're not consistent about whether we call `markRef` in the begin phase or the complete phase. For some fiber types, I found that `markRef` was called in both phases, causing redundant work. After some investigation, I don't believe it's necessary to call `markRef` in both the begin phase and the complete phase, as long as you don't bail out before calling `markRef`. I though that maybe it had to do with the `attemptEarlyBailoutIfNoScheduledUpdates` branch, which is a fast path that skips the regular begin phase if no new props, state, or context were passed. But if the props haven't changed (referentially — the `memo` and `shouldComponentUpdate` checks happen later), then it follows that the ref couldn't have changed either. This is true even in the old `createElement` runtime where `ref` is stored on the element instead of as a prop, because there's no way to pass a new ref to an element without also passing new props. You might argue this is a leaky assumption, but since we're shifting ref to be just a regular prop anyway, I think it's the correct way to think about it going forward. I think the pattern of calling `markRef` in the complete phase may have been left over from an earlier iteration of the implementation before the bailout logic was structured like it is today. So, I removed all the `markRef` calls from the complete phase. In the case of ScopeComponent, which had no corresponding call in the begin phase, I added one. We already had a test that asserted that a ref is reattached even if the component bails out, but I added some new ones to be extra safe. The reason I'm changing this this is because I'm working on a different change to move the ref handling logic in `coerceRef` to happen in render phase of the component that accepts the ref, instead of during the parent's reconciliation.
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.