Callback Functions — JS Technical Interview Questions & Answers

Passing a function to run after another finishes.

Callback Functions

  • Callback Functions (js) is a JS topic. In plain words you use it for add(a, b) in a checkout total. Don’t start with a slogan — start with that picture.
  • Smallest example: function add / const add = () =>. Type it, run it, and say what you see. If you can do that from memory, you know Callback Functions (js).
  • From the example next to this theory: Passing a function to run after another finishes.
  • Trap: this surprise in arrow vs function. Fix that before you talk about advanced JS.
  • Viva: what is Callback Functions (js)? Then show function add / const add = () =>. Then name the trap.

Technical Interview Tip: What is Callback Functions (js)? Show this: function add / const add = () =>. Trap: this surprise in arrow vs function.

Code Examples for Callback Functions

Callback Functions — working example

function greet(name = "friend") {
  return "Hi " + name;
}
const shout = function (msg) {
  return msg.toUpperCase();
};
(function () {
  console.log("IIFE ran");
})();

function mapNums(nums, fn) {
  const out = [];
  for (const n of nums) out.push(fn(n));
  return out;
}
console.log(greet("Ada"), shout("js"));
console.log(mapNums([1, 2], (n) => n * 2));

function factorial(n) {
  if (n <= 1) return 1;
  return n * factorial(n - 1);
}
console.log(factorial(4));

Callback Functions — functions take parameters, can be expressions/IIFEs/callbacks, and recurse with a base case. Pure functions avoid side effects.

How to Explain Callback Functions to an Interviewer

What is Callback Functions (js)?

Used for add(a, b) a checkout total Not just the heading

Give one small example of Callback Functions (js).

function add / const add = () => Passing a function to run after another finishes

What mistake do beginners make with Callback Functions (js)?

this surprise in arrow vs function Show the fix

Where do you use Callback Functions (js)?

a checkout total add(a, b)