Introduction

JavaScript (JS) is a high-level, interpreted programming language used to make web pages interactive — handling user events, updating content dynamically, validating forms, and much more.

1. Embedding JavaScript

a) Inline

<button onclick="alert('Clicked!')">Click Me</button>

b) Internal (inside <script> tag)

<script>
  console.log("Hello, world!");
</script>

c) External (best practice)

<script src="script.js"></script>

2. Output Methods

Method	Description
console.log()	Logs to browser console
alert()	Shows popup alert
document.write()	Writes directly to the document (not recommended)
innerText / innerHTML	Updates page content

console.log("Debug message");
alert("Welcome!");

3. Variables

let name = "Aman";
const PI = 3.14;
var age = 15;

• let – block-scoped (preferred)
• const – cannot be reassigned
• var – function-scoped (avoid using)

4. Data Types

• String — "Hello"
• Number — 42, 3.14
• Boolean — true, false
• Null — null
• Undefined — undefined
• Object — { key: "value" }
• Array — [1, 2, 3]

let x = "Hi";           // string
let y = 123;            // number
let isActive = true;    // boolean
let user = { name: "Aman", age: 16 }; // object

5. Comments

// Single-line comment

/*
  Multi-line
  comment
*/

6. Basic Operators

let a = 5 + 3;     // 8
let b = 10 - 4;    // 6
let c = 2 * 3;     // 6
let d = 8 / 2;     // 4
let e = 9 % 4;     // 1
let f = 2 ** 3;    // 8 (exponent)

7. Basic DOM Manipulation

<p id="demo">Text</p>
<script>
  document.getElementById("demo").innerText = "Changed!";
</script>

JavaScript can select, modify, and respond to HTML elements.

8. Why JavaScript?

• Runs in the browser (no install needed)
• Works with HTML & CSS for full interactivity
• Essential for modern web apps (forms, animation, logic, APIs)