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React transpiles some of its own `console.error` calls into a helper that appends component stacks to those calls. However, this doesn't cover user space `console.error` calls - which includes React helpers that React has moved into third parties like createClass and prop-types. The idea is that any user space component can add a warning just like React can which is why React DevTools adds them too if they don't already exist. Having them appended in both places is tricky because now you have to know whether to remove them from React's logs. Similarly it's often common for server-side frameworks to forget to cover the `console.error` logs from other sources since React DevTools isn't active there. However, it's also annoying to get component stacks clogging the terminal - depending on where the log came from. In the future `console.createTask()` will cover this use case natively and when available we don't append them at all. The new strategy relies on either: - React DevTools existing to add them to React logs as well as third parties. - `console.createTask` being supported and surfaced. - A third party framework showing the component stack either in an Error Dialog or appended to terminal output. For a third party to be able to implement this they need to be able to get the component stack. To get the component stack from within a `console.error` call you need to use the `React.captureOwnerStack()` helper which is only available in `enableOwnerStacks` flag. However, it's possible to polyfill with parent stacks using internals as a stop gap. There's a question of whether React 19 should just go out with `enableOwnerStacks` to expose this but regardless I think it's best it doesn't include component stacks from the runtime for consistency. In practice it's not really a regression though because typically either of the other options exists and error dialogs don't implement `console.error` overrides anyway yet. SSR terminals might miss them but they'd only have them in DEV warnings to begin with an a subset of React warnings. Typically those are either going to happen on the client anyway or replayed. Our tests are written to assert that component stacks work in various scenarios all over the place. To ensure that this keeps working I implement a "polyfill" that is similar to that expected a server framework might do - in `assertConsoleErrorDev` and `toErrorDev`. This PR doesn't yet change www or RN since they have their own forks of consoleWithStackDev for now.
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.