facebook/react

Getting started

This page covers the runtime monorepo (everything outside compiler/). For the React Compiler, see compiler/index — it has its own setup steps.

Prerequisites

Node.js — the version pinned in .nvmrc. Use nvm use if you have nvm installed.
Yarn 1 (Classic). The repo uses yarn@1.22.22, declared in package.json's packageManager field.
Roughly 5–10 GB of disk for node_modules plus build artifacts after a full yarn build.

The repo does not support npm or Yarn 2/3/4 for top-level workspace operations. The compiler/ workspace happens to use a slightly different toolchain but is also Yarn 1.

Cloning and installing

git clone https://github.com/facebook/react.git
cd react
yarn install

yarn install runs the postinstall script node ./scripts/flow/createFlowConfigs.js, which materializes Flow configs for each renderer (the runtime is type-checked with Flow, the compiler with TypeScript).

Building

# Build every package, every channel, every bundle type. Slow (minutes).
yarn build

# Build a focused subset. Useful when iterating on a specific package.
yarn build react/index,react-dom/index,react-dom/client,scheduler --type=NODE_DEV

# Build for the React DevTools extension (also experimental channel).
yarn build-for-devtools-dev

Output lands in build/ and is sub-divided by release channel (e.g. build/oss-stable/react, build/oss-experimental/react, build/facebook-www/). The full taxonomy lives in scripts/rollup/build.js.

Running tests

The test command always goes through the bespoke runner in scripts/jest/jest-cli.js, which sets up release-channel and feature-flag environment variables before delegating to Jest:

# Default: the "experimental" channel — most internal tests.
yarn test

# Stable channel only.
yarn test-stable

# Facebook www modern / classic channels.
yarn test-www
yarn test-classic

# Run tests against the built bundles instead of the source.
yarn test --build

# Run a single test file.
yarn test packages/react-reconciler/src/__tests__/ReactHooks-test.js

# Watch mode and pattern matching are supported.
yarn test -t "useState"

yarn test is what CI runs, parameterized across channels in .github/workflows/runtime_build_and_test.yml. There is no npm test.

Lint, types, format

# ESLint over the whole repo. The config is .eslintrc.js + custom rules in scripts/eslint-rules/.
yarn lint

# Run only against changed files (used as a pre-push gate).
yarn linc

# Flow type check for the runtime. (Compiler uses TypeScript; see compiler/CLAUDE.md.)
yarn flow

# Prettier — write changed files only.
yarn prettier

# Prettier — rewrite everything.
yarn prettier-all

Manual smoke-testing fixtures

fixtures/ contains standalone, runnable React apps that the team uses to verify each renderer end-to-end. Notable ones:

fixtures/dom/ — the all-in-one DOM playground; pulls a fresh build from build/.
fixtures/legacy-jsx-runtimes/ — verifies JSX runtime behavior across Babel versions.
fixtures/flight/ — RSC integration test apps (webpack, parcel, turbopack, esm, unbundled).
fixtures/devtools/ — a fixture used by the DevTools E2E tests.

Each fixture has its own package.json and is installed/built separately.

Recommended IDE setup

The repo ships a VS Code workspace at react.code-workspace. It opens both the runtime and the compiler workspaces side-by-side. Recommended extensions: ESLint, Flow Language Support, Prettier, GitLens.