What is the difference between uncaughtException and unhandledRejection in Node.js and what is the right action when they occur?

Short answer

uncaughtException occurs on a synchronous error not caught by try/catch and the process should be terminated then, while unhandledRejection occurs when a promise fails with no catch handler.

Explanation

When an unhandled synchronous exception is thrown, the Node.js application's state becomes unstable and unguaranteed; the officially recommended action is to log the error, gracefully close the current connections, then terminate the process (process.exit(1)) and let the process manager restart it.

Code example

process.on("uncaughtException", (err) => {
  console.error("Critical error:", err);
  process.exit(1);
});

Common mistakes

• Trying to continue running the server after an uncaughtException, which leads to data corruption or a memory leak.

Follow-up questions

• How do you design a graceful shutdown mechanism in a Node.js app when receiving SIGTERM or SIGINT signals?

Sources

• Node.js docs — process: Event 'uncaughtException'
• Node.js docs — process: Event 'unhandledRejection'