Day 3 Data Types
JavaScript mein har value ka ek type hota hai. Yeh types define karte hain ke value ke saath kya operations kar sakte hain.
Primitive Types
6 basic primitive types hote hain JavaScript mein:
// 1. String — text
let name = "CodingSkillUp";
let greeting = 'Hello World';
let template = `My name is ${name}`; // template literal
// 2. Number — integers aur decimals
let age = 25;
let price = 9.99;
let negative = -10;
// 3. Boolean — true ya false
let isLoggedIn = true;
let hasError = false;
// 4. Undefined — variable declared but no value
let notAssigned;
console.log(notAssigned); // undefined
// 5. Null — intentionally empty
let emptyValue = null;
// 6. BigInt — very large numbers
let bigNumber = 9007199254740991n;
typeof Operator
typeof se kisi bhi value ka type check kar sakte hain.
console.log(typeof "hello"); // "string"
console.log(typeof 42); // "number"
console.log(typeof true); // "boolean"
console.log(typeof undefined); // "undefined"
console.log(typeof null); // "object" ← JS ka famous bug!
console.log(typeof {}); // "object"
console.log(typeof []); // "object"
console.log(typeof function(){}); // "function"
Type Conversion
JavaScript automatically types convert karta hai (Type Coercion). Iska ilm zaroori hai.
// Implicit conversion (JS khud karta hai)
console.log("5" + 3); // "53" (string + number = string)
console.log("5" - 3); // 2 (JS converts string to number)
console.log(true + 1); // 2 (true = 1)
console.log(false + 1); // 1 (false = 0)
// Explicit conversion (hum karte hain)
let numStr = "42";
let num = Number(numStr); // 42
let str = String(100); // "100"
let bool = Boolean(0); // false
let bool2 = Boolean("hi"); // true
🎯 Practice Challenge
Har type ka ek variable banao. typeof se sab check karo. '5' + 5 aur '5' - 5 dono try karo.