Variables aur Data Types

Variable ek naam hai jo ek value ki taraf ishara karta hai. JavaScript mein variable declare karne ke teen tareeqe hain — let, const, aur purana var — aur aap kaunsa chunte hain yeh asal mein maqsad rakhta 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 tor par istemal karo
• let ek aisa variable banata hai jise reassign kiya ja sakta hai — isko tabhi istemal karo jab value waqai badalni chahiye
• var variables declare karne ka purana tareeqa hai, let/const aane se pehle ka — naye code mein isse bacho, iske scoping rules confusing hain

Core data types

typeof batata hai ke koi value asal mein 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 to 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

Ghor karo typeof null "object" wapas karta hai — yeh JavaScript ka ek mash'hoor, purana quirk hai (backward compatibility ke liye rakha gaya), iska matlab yeh nahi ke null asal mein ek object hai. Ise ek khaas value samjho jiska matlab hai "jaan boojh kar kuch nahi".

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