How to fix PropTypes is not part of the React namespace in React

React 19 Changes: React 19 removes propTypes and defaultProps support for function components entirely. If you're using React 19+, consider migrating to TypeScript or another static type-checking solution instead of runtime PropTypes validation.

TypeScript Migration: For modern React projects, TypeScript is the recommended approach for type safety:

interface UserCardProps {
  name: string;
  age: number;
  email?: string;
}

function UserCard({ name, age, email }: UserCardProps) {
  return (
    <div>
      <h2>{name}</h2>
      <p>Age: {age}</p>
      {email && <p>Email: {email}</p>}
    </div>
  );
}

TypeScript provides compile-time type checking, better IDE support, and doesn't add runtime overhead like PropTypes does.

Performance Considerations: PropTypes validation only runs in development mode and is stripped out in production builds (when using proper build tools). However, the prop-types package still needs to be bundled, adding a small amount to your bundle size (~7KB minified).

Class Components: PropTypes still work with class components in React 19, but are removed for function components. If you must use PropTypes with function components in React 19+, you'll need to convert them to class components or use an older React version.

Codemod Tools: React provides several codemods to help with migrations:
- React-PropTypes-to-prop-types: Converts React.PropTypes to the separate package
- types-react-codemod: Helps with React 19 migration including PropTypes removal

Run with: npx types-react-codemod@latest preset-19 ./src