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In the next major release, we intend to drop support for using the `act` testing helper in production. (It already fires a warning.) The rationale is that, in order for `act` to work, you must either mock the testing environment or add extra logic at runtime. Mocking the testing environment isn't ideal because it requires extra set up for the user. Extra logic at runtime is fine only in development mode — we don't want to slow down the production builds. Since most people only run their tests in development mode, dropping support for production should be fine; if there's demand, we can add it back later using a special testing build that is identical to the production build except for the additional testing logic. One blocker for removing production support is that we currently use `act` to test React itself. We must test React in both development and production modes. So, the solution is to fork `act` into separate public and internal implementations: - *public implementation of `act`* – exposed to users, only works in development mode, uses special runtime logic, does not support partial rendering - *internal implementation of `act`* – private, works in both development and productionm modes, only used by the React Core test suite, uses no special runtime logic, supports partial rendering (i.e. `toFlushAndYieldThrough`) The internal implementation should mostly match the public implementation's behavior, but since it's a private API, it doesn't have to match exactly. It works by mocking the test environment: it uses a mock build of Scheduler to flush rendering tasks, and Jest's mock timers to flush Suspense placeholders. --- In this first commit, I've added the internal forks of `act` and migrated our tests to use them. The public `act` implementation is unaffected for now; I will leave refactoring/clean-up for a later step.
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.