function test() {
    var age = 25;
    console.log(age);
}

age

cannot be accessed outside

test()

.

Block Scope

let

and

const

are block-scoped.

if (true) {
    let x = 10;
    const y = 20;
    console.log(x, y);
}

x

and

y

cannot be accessed outside the

if

block.

18. What is strict mode ("use strict")?

Strict mode enables a stricter set of JavaScript rules and helps catch certain programming mistakes.

Example:

"use strict";
x = 10;

This produces a

ReferenceError

because

x

was not declared. 

Without strict mode, older JavaScript behavior could create a global variable in some situations.

Benefits:

Catches common mistakes

Prevents accidental global variables

Makes some unsafe operations throw errors

Helps write cleaner code

19. What are comments in JavaScript?

Comments are text ignored by the JavaScript engine. They are used to explain code or temporarily disable code.

Single-Line Comment:

// This is a comment
console.log("Hello");

Multi-Line Comment:

/*
   This is a
   multi-line comment
*/
console.log("Hello");

Why Use Comments?

✅ Explain complex logic

✅ Improve code readability

✅ Help other developers understand the code

✅ Document important decisions

20. What are JavaScript modules?

Modules allow you to split JavaScript code into separate, reusable files.

They help organize large applications and prevent unnecessary global variables.

Export:

// math.js
export function add(a, b) {
    return a + b;
}

Import:

// app.js
import { add } from "./math.js";
console.log(add(10, 20));

Types of Exports:

Named exports

Default exports

Default Export:

export default function greet() {
    console.log("Hello");
}

Important Interview Point:

ES Modules use

import

and

export

. They are the standard module system for modern JavaScript.

❤️ Double Tap For Part 3