JavaScript Kya Hai?
JavaScript ek programming language hai jo browsers mein chalti hai (aur ab Node.js se server par bhi) — HTML/CSS jo "kaisa dikhta hai" define karte hain, JavaScript "kya HOTA hai" define karta hai — button click karne par kya ho, form submit karne par kya check ho, waghera.
JavaScript "interpreted" hai (C/Java jaisa compile step nahi, browser directly chalata hai) aur "dynamically typed" hai (Python jaisa — variable ka type declare karne ki zaroorat nahi). Ye web ki EK-AUR-ONLY language hai jo har browser natively samajhta hai.
JavaScript ko HTML mein <script> tag se include karte hain — src attribute se external file (best practice), ya seedha tag ke andar inline code.
<script src="script.js"></script>
<!-- script.js: -->
console.log("Hello, JavaScript!");
let name = "Aarav";
alert("Welcome, " + name);- JavaScript = interactivity/behavior layer, HTML=structure, CSS=style
- Interpreted, dynamically-typed — browser mein directly chalta hai
- <script src="..."> se HTML mein include karte hain
"JavaScript" naam marketing decision tha (1995 mein, jab Java popular tha) — dono languages ka syntax thoda similar dikhta hai (curly braces, semicolons), lekin design, purpose, aur execution model completely different hain. Ek common beginner confusion hai inhe related samajhna.
// JavaScript — dynamically typed, browser mein chalta hai:
let x = 5;
x = "now a string"; // valid, type change ho sakta hai
// Java — statically typed, compiled:
// int x = 5;
// x = "now a string"; // COMPILE ERROR — type fixed haiNode.js JavaScript ko browser ke bahar (server par, ya command line par) chalane deta hai — 2009 mein aaya, JavaScript ko sirf "frontend language" se "full-stack language" bana diya (backend servers, tools, scripts sab JavaScript mein ban sakte hain).
// Terminal mein:
// $ node script.js
// script.js:
console.log("Ye Node.js mein chal raha hai, browser mein nahi!");