What is JavaScript & How It Works

What is JavaScript?

What JavaScript Can Do

• Change HTML content dynamically — show/hide elements, update text, modify styles
• Respond to user actions — clicks, keyboard input, mouse movements, form submissions
• Validate form inputs before sending to the server — instant feedback without page reload
• Fetch data from APIs — load content, display live data, communicate with servers
• Create animations and visual effects — smooth transitions, scroll effects, interactive UI
• Build complete web applications — React, Vue, Angular are all JavaScript frameworks
• Run on servers with Node.js — one language for both frontend and backend

Your First JavaScript

// JavaScript runs in the browser console (press F12)
console.log("Hello, World!");
console.log("Welcome to JavaScript!");

// JavaScript can do math
console.log(10 + 5);    // 15
console.log(100 * 2);   // 200

// JavaScript can work with text
console.log("My name is " + "Alice");

// JavaScript can make decisions
if (10 > 5) {
  console.log("10 is greater than 5!");
}

Try It Yourself: Hello World

// console.log() prints output to the console
console.log("Hello, World!");
console.log("I am learning JavaScript!");

// You can print numbers
console.log(42);
console.log(3.14);

// And calculations
console.log(10 + 5);
console.log(100 - 37);
console.log("10 + 5 =", 10 + 5);

// Try changing the messages above and click Run!

Tip

Common Mistake

Practice Task

Quick Quiz