Function Basics — JS Technical Interview Questions & Answers

Declaring, calling and returning values from functions.

Function Basics

  • Declaring, calling and returning values from functions.
  • function add(a, b) { return a + b; } add(2, 3) is 5. If you forget return, you get undefined. Arrow: const add = (a, b) => a + b;
  • Parameters are inputs. Arguments are the values you pass. Default: function hi(name = 'student').
  • Trap: missing return. Trap: this inside an arrow vs a method — learn that with DOM later.

Technical Interview Tip: function add(a,b){ return a+b } Don’t forget return.

Code Examples for Function Basics

Function Basics — 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));

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

How to Explain Function Basics to an Interviewer

What if you omit return?

The function gives undefined