JavaScript Basics

🌐 What is JavaScript and How It Works?
JavaScript is a high-level scripting language used to add functionality to web pages.

👉 It controls how a website behaves.

🔹 Example:

• Button click actions
• Form validations
• Showing alerts
• Animations
• Dynamic content updates

🧠 Where JavaScript is Used?

• 🌐 Websites (Frontend)
• ⚙️ Server-side apps (Node.js)
• 📱 Mobile apps (React Native)
• 🎮 Games and interactive apps

⚙️ How JavaScript Works?

JavaScript runs inside a web browser.

🔹 Step-by-step working:

1. You write JavaScript code

Example:

console.log("Hello World");

2. Browser receives the code

When you open a webpage, the browser loads HTML, CSS, and JavaScript.

3. JavaScript engine executes it

Every browser has a JavaScript Engine:

Chrome → V8 engine
Firefox → SpiderMonkey
Safari → JavaScriptCore

4. Code is executed line by line

JavaScript is interpreted, so it runs step by step.

5. Output is shown

Example output:
Hello World

Simple Real-Life Example

👉 Think of a website like a car:

• HTML → Structure (body of car)
• CSS → Design (paint & look)
• JavaScript → Engine (makes it move)

⚡ Important Features of JavaScript

• Runs in browser
• Easy to learn
• Lightweight language
• Supports dynamic behavior
• Works with HTML & CSS

🎯 Example Program

let name = "Akalya";

console.log("Welcome " + name);

Output:

Welcome Akalya

🧠 Data Types in JavaScript

JavaScript has two main types of data:

🔹 1. Primitive Data Types

• Number → 10, 20
• String → "Hello"
• Boolean → true, false
• Undefined → variable declared but not assigned
• Null → empty value

Example:

let age = 20;
let name = "JS";
let isStudent = true;

🔹 2. Non-Primitive Data Types

• Array → list of values
• Object → collection of key-value pairs

Example:

let numbers = [1, 2, 3];

let person = {
  name: "John",
  age: 25
};

✍️ Variables in JavaScript

Variables are used to store data.

We can declare variables using:

🔹 var

var x = 10;

🔹 let

let y = 20;

🔹 const

const z = 30;

Difference Between var, let, const
var

• Old method
• Can redeclare
• Can change value

let

• Modern
• Cannot redeclare
• Can change value

const

• Constant
• Cannot redeclare
• Cannot change value

🎯 Simple Example

let name = "JavaScript";
const version = 2024;

console.log(name);
console.log(version);