How do you handle errors in Node.js, including in async code and at the process level?

Node has several error channels and you need to cover all of them.

• Synchronous code — try/catch.
• Promises and async/await — try/catch around the await, or .catch() on the chain. In Express 4 an async route handler that throws is not caught by the framework, so you need a wrapper that forwards the rejection to next(err); Express 5 handles it natively.
• Callbacks — the error-first convention, (err, result). Check err before anything else and return early.
• EventEmitters — listen for the 'error' event. An unhandled 'error' event throws and crashes the process, which is deliberate.

At the process level: attach handlers for uncaughtException and unhandledRejection, but use them only to log and then exit cleanly — not to keep running. After an uncaught exception the process is in an unknown state, and continuing risks corrupting data.

Note: Distinguish operational errors, such as a failed network call, which you handle and retry, from programmer errors such as a TypeError, which you should let crash so a supervisor restarts the process.