React 19 Source Migration Patterns
Reference for every source-file migration required for React 19.
Quick Reference Table
| Pattern | Action | Reference |
|---|---|---|
| ReactDOM.render(...) | → createRoot().render() | See references/api-migrations.md |
| ReactDOM.hydrate(...) | → hydrateRoot(...) | See references/api-migrations.md |
| unmountComponentAtNode | → root.unmount() | Inline fix |
| ReactDOM.findDOMNode | → direct ref | Inline fix |
| forwardRef(...) wrapper | → ref as direct prop | See references/api-migrations.md |
| Component.defaultProps = {} | → ES6 default params | See references/api-migrations.md |
| useRef() no arg | → useRef(null) | Inline fix add null |
| Legacy Context | → createContext | → api-migrations.md#legacy-context |
| String refs this.refs.x | → createRef() | → api-migrations.md#string-refs |
| import React from 'react' (unused) | Remove | Only if no React. usage in file |
PropTypes Rule
Do not remove .propTypes assignments. The prop-types package still works as a standalone validator. React 19 only removes the built-in runtime checking from the React package the package itself remains valid.
Add this comment above any .propTypes block:
// NOTE: React 19 no longer runs propTypes validation at runtime.
// PropTypes kept for documentation and IDE tooling only.
Read the Reference
For full before/after code for each migration, read references/api-migrations.md. It contains the complete patterns including edge cases for forwardRef with useImperativeHandle, defaultProps null vs undefined behavior, and legacy context provider/consumer cross-file migrations.