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## Summary There is a bug in the `react-hooks/exhaustive-deps` rule that forbids the dependencies argument from being `undefined`. It triggers the error that the dependency list is not an array literal. This makes sense in pre ES5 strict-mode environments as undefined could be redefined, but should not be a concern in today's JS environments. **Justification:** * The deps argument being undefined (for `useEffect` calls etc.) is a valid use case for hooks that should re-run on every render. * The deps argument being omitted is considered a valid use case by the `exhaustive-deps` rule already. * The TypeScript type definitions support passing `undefined` because hooks are typed as `useEffect(effect: EffectCallback, deps?: DependencyList): void;`. * Since omitting an argument and passing `undefined` are considered equivalent, this eslint rule should consider them as equivalent too. Further, I accidentally forgot passing a dependency array to `useEffect` in code that I shared on Twitter, and people started abusing me about it. I'd like to create an eslint rule for my projects that requires me to provide a dep argument in all cases (`undefined`, `[]` or the list of dependencies) so that I can avoid such problems in the future. This would also force me to always think about the dependencies instead of accidentally forgetting them and my hook running on each render. In an audit of my own codebase I had about 3% of hooks that I want to run on each render, and adding an explicit `undefined` seems reasonable in those situations. It could be argued this could be an option or part of the `exhaustive-deps` rule, but it's probably better to merge this PR, make a release and see if my custom eslint rule gains traction in the future. ## How did you test this change? * Added a test. * `yarn test ESLintRuleExhaustiveDeps-test` * Careful code inspection.
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 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.