javascript/Error Handling

try/catch/finally handles synchronous errors, but most real bugs in JavaScript aren't synchronous — they're a rejected promise three layers deep in an async chain, or a callback that throws after the surrounding try block has already finished executing. try/catch only catches errors thrown while it's actively running, which is exactly why wrapping a setTimeout or an unawaited promise in try/catch silently does nothing.

Good error handling also means throwing the right kind of error, not just any error. Extending the built-in Error class to create custom error types (ValidationError, NetworkError) lets calling code branch on error.name or instanceof instead of parsing a message string. And errors that go unhandled don't just disappear — an uncaught synchronous throw crashes the process (in Node) or halts execution, while an unhandled promise rejection fires a separate, easy-to-miss event that many apps never listen for.