A declarative, efficient, and flexible JavaScript library for building user interfaces. reactjs.org
Go to file
Sebastian Markbåge 2a911f27dd
[Flight] Send the awaited Promise to the client as additional debug information (#33592)
Stacked on #33588, #33589 and #33590.

This lets us automatically show the resolved value in the UI.

<img width="863" alt="Screenshot 2025-06-22 at 12 54 41 AM"
src="https://github.com/user-attachments/assets/a66d1d5e-0513-4767-910c-5c7169fc2df4"
/>

We can also show rejected I/O that may or may not have been handled with
the error message.

<img width="838" alt="Screenshot 2025-06-22 at 12 55 06 AM"
src="https://github.com/user-attachments/assets/e0a8b6ae-08ba-46d8-8cc5-efb60956a1d1"
/>

To get this working we need to keep the Promise around for longer so
that we can access it once we want to emit an async sequence. I do this
by storing the WeakRefs but to ensure that the Promise doesn't get
garbage collected, I keep a WeakMap of Promise to the Promise that it
depended on. This lets the VM still clean up any Promise chains that
have leaves that are cleaned up. So this makes Promises live until the
last Promise downstream is done. At that point we can go back up the
chain to read the values out of them.

Additionally, to get the best possible value we don't want to get a
Promise that's used by internals of a third-party function. We want the
value that the first party gets to observe. To do this I had to change
the logic for which "await" to use, to be the one that is the first
await that happened in user space. It's not enough that the await has
any first party at all on the stack - it has to be the very first frame.
This is a little sketchy because it relies on the `.then()` call or
`await` call not having any third party wrappers. But it gives the best
object since it hides all the internals. For example when you call
`fetch()` we now log that actual `Response` object.
2025-06-23 10:12:45 -04:00
.codesandbox Build react-server-dom-webpack for codesandbox (#32990) 2025-04-22 22:20:21 +02:00
.github Make it clearer what runtime release failed (#33579) 2025-06-20 09:11:27 +02:00
compiler [compiler] Cleanup debugging code (#33571) 2025-06-18 16:00:55 -07:00
fixtures [Flight] Send the awaited Promise to the client as additional debug information (#33592) 2025-06-23 10:12:45 -04:00
packages [Flight] Send the awaited Promise to the client as additional debug information (#33592) 2025-06-23 10:12:45 -04:00
scripts Expose cacheSignal() alongside cache() (#33557) 2025-06-17 17:04:40 -04:00
.editorconfig Remove trim_trailing_whitespace from editorconfig (#31413) 2024-11-04 15:30:02 -05:00
.eslintignore Fix ESLint and Prettier configs for React Compiler (#29073) 2024-05-15 14:02:57 -07:00
.eslintrc.js [Flight] Forward debugInfo from awaited instrumented Promises (#33415) 2025-06-04 00:49:03 -04:00
.git-blame-ignore-revs Add run prettier commit to .git-blame-ignore-revs 2024-07-18 17:42:45 -04:00
.gitattributes .gitattributes to ensure LF line endings when we should 2014-01-17 16:25:53 -08:00
.gitignore [forgive] Init (#31918) 2025-02-25 12:19:11 -05:00
.mailmap updates mailmap entries (#19824) 2020-09-12 13:05:52 -04:00
.nvmrc Upgrade node.js to 20 LTS (#32855) 2025-04-14 12:52:02 -04:00
.prettierignore [prettier] Ignore compiler/target (#31168) 2024-10-10 10:53:27 -04:00
.prettierrc.js [scripts] Switch back to flow parser for prettier (#33414) 2025-06-03 00:00:28 -04:00
.watchmanconfig .watchmanconfig must be valid json (#16118) 2019-07-11 19:01:02 -07:00
babel.config-react-compiler.js feat(eslint-plugin-react-hooks): merge rule from eslint-plugin-react-compiler into react-hooks plugin (#32416) 2025-03-12 21:43:06 -04:00
babel.config-ts.js Update babel configs used in jest (#32588) 2025-03-12 19:07:39 -04:00
babel.config.js Partially revert #32588 (#32621) 2025-03-15 15:21:57 -04:00
CHANGELOG.md Update 19.1 changelog to remove confusing owner stack sentance 2025-03-28 14:55:28 -07:00
CODE_OF_CONDUCT.md revert last grammatical edit (#25067) 2022-08-10 20:14:31 +01:00
CONTRIBUTING.md Fix: Updated link in CONTRIBUTING (#25381) 2022-10-03 10:29:57 -04:00
dangerfile.js Fix typo in dangerfile.js which results in an unreachable code path… (#32277) 2025-01-31 01:44:02 -05:00
LICENSE [Codemod] Update copyright header to Meta (#25315) 2022-10-18 11:19:24 -04:00
MAINTAINERS Update MAINTAINERS (#32238) 2025-01-27 13:40:45 -06:00
package.json [tests] remove pretest compiler script (#33452) 2025-06-06 09:16:58 -04:00
react.code-workspace created a vscode workspace file for the repo (#29830) 2024-06-13 16:23:42 +01:00
ReactVersions.js [eprh] Bump stable version (#32978) 2025-04-21 14:36:13 -04:00
README.md [ez] Remove circleci badge from readme 2024-07-29 13:26:14 -04:00
SECURITY.md Create SECURITY.md (#15784) 2020-01-09 14:07:41 -08:00
yarn.lock [scripts] Switch back to flow parser for prettier (#33414) 2025-06-03 00:00:28 -04:00

React · GitHub license npm version (Runtime) Build and Test (Compiler) TypeScript PRs Welcome

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:

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.

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.