How do errors travel in asynchronous code and what is the danger of errors inside traditional callbacks?

Short answer

Promise errors travel through rejection chains, while outer try/catch blocks fail to catch errors inside traditional callbacks, causing the server to crash.

Explanation

A try/catch block protects only synchronous code executed in the same call stack. If an asynchronous function that accepts a traditional callback is called and an exception is thrown inside it with throw, the original stack has already ended, and the error goes straight to uncaughtException.

Code example

import { readFile } from "node:fs/promises";
const data = await readFile("file.txt");

Common mistakes

• Throwing errors with throw inside a regular callback function instead of passing them to the first parameter (err).

Follow-up questions

• What is the practical difference between using async/await and dealing directly with promises in Node.js?

Sources

• Node.js docs — Errors