What is the difference between callbacks and Promises in Node.js?

Direct answer

Callbacks (err, result) nest and require manual error propagation at each step; Promises chain with .then/catch or async/await with centralized error handling — modern Node favors Promises and fs.promises, but libuv and streams still expose callback and event APIs underneath.

Callbacks were Node's original async style — Promises (ES2015) and async/await layered on top without removing the event-loop + callback foundation.

Aspect	Callbacks	Promises
Error handling	if (err) at every level	.catch / try/catch once
Composition	Callback hell / pyramid	Chain or Promise.all
Cancellation	Manual flags	AbortSignal (modern)
Node APIs	Legacy fs, some crypto	fs/promises, fetch, pipeline

Error-first convention — (err, data) =>; omitting err check is a classic bug.
Callback hell — nested readFile → parse → query → respond.
Promisify bridge — Q59 connects legacy to modern style.

callback-vs-promise.mjs

// Callback style
fs.readFile("config.json", "utf8", (err, raw) => {
  if (err) return console.error(err);
  const config = JSON.parse(raw);
  db.connect(config.url, (err2) => {
    if (err2) return console.error(err2);
    // ...
  });
});

// Promise style
const raw = await fs.readFile("config.json", "utf8");
const config = JSON.parse(raw);
await db.connect(config.url);