JavaScript Introduction

What is JavaScript?

• A lightweight, interpreted programming language.
• Runs inside browsers (client-side) and also on servers (Node.js).
• Used for dynamic content, form validation, animations, and full web apps.

Key Features of JavaScript

• Dynamic typing (no need to declare types explicitly).
• Prototype-based object system.
• First-class functions (can be stored, passed, returned).
• Event-driven and asynchronous programming support.
• Modern ES6+ features (arrow functions, classes, modules, promises).

// 1) Alert box
<script>
  alert('Hello World!');
</script>

// 2) Console log (DevTools)
<script>
  console.log('Hello Console!');
</script>

// 3) Write into HTML
<div id="demo"></div>
<script>
  document.getElementById('demo')
    .innerHTML = 'Hello Page!';
</script>

Where Does JavaScript Run?

Originally built for browsers, JS now runs almost everywhere:

• Browser: Chrome, Firefox, Edge, Safari (via JavaScript engines like V8, SpiderMonkey)
• Server: Node.js (built on V8)
• Desktop & Mobile Apps: via frameworks like Electron, React Native
• IoT & More: JS engines embedded in devices

A Short History

• 1995 – Created by Brendan Eich at Netscape in just 10 days.
• 1997 – Standardized as ECMAScript (ES).
• 2009 – Node.js made JS run on servers.
• 2015 – ES6 (ECMAScript 2015) brought classes, modules, arrow functions, let/const.
• Today – Evolving yearly with new features.