Variables aur Data Types

Variable ek naam hai jo ek value ko point karta hai. JavaScript mein variable declare karne ke teen tarike hain — let, const, aur purana var — aur aap kaunsa choose karte ho yeh actually matter karta hai.

let name = "Alice";
const age = 30;
let isStudent = false;

console.log(name, typeof name);
console.log(age, typeof age);
console.log(isStudent, typeof isStudent);

Alice string
30 number
false boolean

let vs. const vs. var

• const ek aisa variable banata hai jise reassign nahi kiya ja sakta — isko default ke roop mein use karo
• let ek aisa variable banata hai jise reassign kiya ja sakta hai — isko tabhi use karo jab value genuinely change honi chahiye
• var variables declare karne ka purana tarika hai, let/const aane se pehle ka — naye code mein isse avoid karo, iske scoping rules confusing hain

Core data types

typeof batata hai ki koi value actually kis type ki hai. JavaScript ke core primitive types hain string (text), number (poore numbers aur decimals dono — JavaScript inhe Python ke int/float ki tarah alag nahi karta), boolean (true ya false), undefined (ek variable jo declare toh ho gaya hai lekin usse koi value nahi di gayi), aur null (jaan boojh kar value na hona).

let score;
console.log(score, typeof score);

let empty = null;
console.log(empty, typeof empty);

undefined undefined
null object

Notice karo typeof null "object" return karta hai — yeh JavaScript ka ek famous, purana quirk hai (backward compatibility ke liye rakha gaya), iska matlab yeh nahi ki null actually ek object hai. Ise ek special value samjho jiska matlab hai "jaan boojh kar kuch nahi".

Aage: numbers — arithmetic operators aur JavaScript ka single number type actually kaise kaam karta hai.