Node.js · Theory

Callbacks

Theory

29/723

Callbacks

Callbacks is a Node.js topic. In plain words you use it for read notes.txt in a script. Don’t start with a slogan — start with that picture.

Smallest example: (err, data) => …. Type it, run it, and say what you see. If you can do that from memory, you know Callbacks.

From the example next to this theory — Callbacks: find user 2, then list names.

Trap — callback hell, no error-first. Fix that before you talk about advanced Node.js.

Viva — what is Callbacks? Then show (err, data) => …. Then name the trap.

Exam tip

What is Callbacks? Show this: (err, data) => …. Trap: callback hell, no error-first.

Example

// Callbacks
const users = [
  { id: 1, name: "Asha" },
  { id: 2, name: "Ravi" },
];

function findUser(id) {
  return users.find((u) => u.id === id) ?? null;
}

console.log(findUser(2));
console.log(users.map((u) => u.name));

Callbacks: find user 2, then list names. Say both prints.

Short notes

DefCallbacks — read notes.txt in a script.
Rule(err, data) => …
Trapcallback hell, no error-first
Usea script

Node.js · Theory

Callbacks

← All stacks

Theory

29/723

Callbacks

Callbacks is a Node.js topic. In plain words you use it for read notes.txt in a script. Don’t start with a slogan — start with that picture.

Smallest example: (err, data) => …. Type it, run it, and say what you see. If you can do that from memory, you know Callbacks.

From the example next to this theory — Callbacks: find user 2, then list names.

Trap — callback hell, no error-first. Fix that before you talk about advanced Node.js.

Viva — what is Callbacks? Then show (err, data) => …. Then name the trap.

Exam tip

What is Callbacks? Show this: (err, data) => …. Trap: callback hell, no error-first.

Example

// Callbacks
const users = [
  { id: 1, name: "Asha" },
  { id: 2, name: "Ravi" },
];

function findUser(id) {
  return users.find((u) => u.id === id) ?? null;
}

console.log(findUser(2));
console.log(users.map((u) => u.name));

Callbacks: find user 2, then list names. Say both prints.

Short notes

DefCallbacks — read notes.txt in a script.
Rule(err, data) => …
Trapcallback hell, no error-first
Usea script

Callbacks

Example

Short notes

Questions

Callbacks

Example

Short notes

Questions