🚀 Web Development Interview Questions with Answers — Part 3: JavaScript

🧠 46. What is JavaScript?

JavaScript is a programming language used to make web pages interactive.

It is used for:

• Form validation

• Dynamic content

• API calls

• Animations

• Interactive UI

Example:

console.log("Hello World");

🧠 47. Difference Between var, let, and const

var : Function scoped

Can redeclare

Can reassign

let : Block scoped

Cannot redeclare

Can reassign

const : Block scoped

Cannot redeclare

Cannot reassign

Example:

var a = 10;

let b = 20;

const c = 30;

🧠 48. What are Data Types in JavaScript?

Primitive Data Types:

• String

• Number

• Boolean

• Null

• Undefined

• Symbol

• BigInt

Non-Primitive:

• Object

• Array

• Function

Example:

let name = "Sanyam";

let age = 26;

let isActive = true;

🧠 49. Difference Between null and undefined

null : Intentional empty value

undefined : Variable declared but not assigned

Example:

let a = null;

let b;

console.log(b);

🧠 50. What is Hoisting?

Hoisting means JavaScript moves declarations to the top before execution.

Example:

console.log(a);

var a = 10;

Output:

undefined

🧠 51. Explain Scope in JavaScript

Scope determines where variables are accessible.

Types:

• Global Scope

• Function Scope

• Block Scope

Example:

{

let age = 26;

}

age cannot be accessed outside block.

🧠 52. What is Closure?

A closure allows a function to access variables from its outer function even after execution.

Example:

function outer() {

let count = 0;

return function inner() {

count++;

console.log(count);

};

}

const fn = outer();

fn();

🧠 53. What is Callback Function?

A callback is a function passed into another function.

Example:

function greet(name, callback) {

console.log(name);

callback();

}

greet("Deepak", function() {

console.log("Welcome");

});

🧠 54. What is Arrow Function?

Arrow functions provide shorter syntax.

Example:

const add = (a, b) => a + b;

Benefits:

✅ Cleaner syntax

✅ Lexical this

🧠 55. Difference Between == and ===

== : Checks value only

=== : Checks value and type

Example:

5 == "5" // true

5 === "5" // false

🧠 56. What is Event Bubbling?

Event bubbling means events move from child to parent.

Example:

button.addEventListener("click", () => {

console.log("Button clicked");

});

🧠 57. What is Event Capturing?

Event capturing is opposite of bubbling.

Event moves: Parent → Child

Example:

element.addEventListener("click", fn, true);

🧠 58. What is Event Delegation?

Using parent element to handle child events.

Benefits:

✅ Better performance

✅ Dynamic elements support

Example:

parent.addEventListener("click", (e) => {

console.log(e.target);

});

🧠 59. What is DOM?

DOM stands for: 👉 Document Object Model

It represents HTML as objects.

Example:

document.getElementById("title");