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.