✅ What is JavaScript?

JavaScript is a programming language used to make websites interactive and dynamic.

👉 Without JavaScript:

Website = Static (only text, images)

👉 With JavaScript:

Buttons respond
Forms validate
Animations work
Data updates without reload

📌 Example:

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

📜 History of JavaScript

Created in 1995 by Brendan Eich
Developed at Netscape
Initially called Mocha, then LiveScript
Finally named JavaScript

👉 Important:

JavaScript is NOT Java
Name was for marketing 😄

📈 Today:

Runs in browsers
Also runs on servers (Node.js)

⚔️ JavaScript vs HTML vs CSS

Technology	Purpose
HTML	Structure (Skeleton)
CSS	Design (Styling)
JavaScript	Behavior (Brain)

👉 Example:

<h1>Hello</h1>      <!-- HTML -->
<style>h1{color:red}</style>  <!-- CSS -->
<script>alert('Hi')</script>  <!-- JavaScript -->

🌐 How JavaScript Works in Browser

Browser loads HTML
Parses HTML → creates DOM
Loads CSS
Executes JavaScript

👉 JavaScript can:

Change HTML
Change CSS
Handle events

📌 Example:

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

⚙️ JavaScript Engines

JavaScript engine = program that runs JS code

Popular Engines:

V8 → Chrome, Edge
SpiderMonkey → Firefox
JavaScriptCore → Safari

👉 What engine does:

Reads code
Converts to machine code
Executes fast

🧪 Writing First JavaScript Program

👉 Example:

console.log("Hello, World!");

📌 Output:

Appears in browser console

👉 Another example:

alert("Welcome to JavaScript!");

🔗 Adding JavaScript to HTML

There are 3 ways:

1️⃣ Inline JavaScript

👉 JS written inside HTML tag

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

📌 Use:

Small actions

❌ Not recommended for large projects

2️⃣ Internal JavaScript

👉 JS written inside <script> tag

<!DOCTYPE html>
<html>
<head>
</head>
<body><script>
  alert("Internal JS");
</script></body>
</html>

📌 Best for:

Small to medium scripts

3️⃣ External JavaScript

👉 JS in separate .js file

HTML:

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

script.js:

alert("External JS");