How do error boundaries work in React and what errors do they not catch?

A class component implementing getDerivedStateFromError and/or componentDidCatch (or framework equivalents) acts as an error boundary: it catches render errors in descendants and can render fallback UI. They do not catch errors in event handlers, async code, SSR errors outside boundaries, or errors in the boundary itself.

Error boundaries are declarative try/catch for the React render phase. For events and async work, use normal try/catch. Place boundaries at route or feature boundaries to isolate failures.