What is the difference between defaultProps and default parameter values?

Both provide fallback values for component props, but they work differently. defaultProps: a static property on the component class or function that React merges with the passed props before rendering. Deprecated for function components in React 18.3. MyComponent.defaultProps = { color: "blue", size: 16 };. Pros: works in class components; was the original React way. Cons: the defaults are defined separately from the component signature, making them less visible; deprecated for function components. Default parameter values: standard JavaScript destructuring defaults in the function signature. function Button({ color = "blue", size = 16, onClick }) { ... }. Pros: co-located with props; type inference works better in TypeScript; more idiomatic modern JavaScript; works for function components without any React-specific API. Cons: does not work in class components. Recommendation: always use JavaScript default parameter values for function components — they are cleaner, more visible, and better supported by tooling. Use defaultProps only if maintaining legacy class components.