JavaScript Me Regular Expressions Kya Hota Hai?

Regular Expressions (RegEx) ka Introduction

Regular Expressions (jise "RegEx" bhi kehte hain) ek powerful tool hai jo strings me patterns ko search, match, aur manipulate karne ke liye use hota hai. Jab aapko kisi string me specific characters, words, ya formats ko dhoondhna ya validate karna ho, toh RegEx bohot kaam aata hai.

RegEx Kaise Banayein?

JavaScript me RegEx banane ke do tarike hain:

1. Literal Notation

Yeh sabse common tarika hai, jisme pattern ko do forward slashes / ke beech likha jaata hai.

let regex = /hello/i; // 'i' flag for case-insensitive search

2. Constructor Method

Aap new RegExp() constructor ka use karke bhi RegEx bana sakte hain.

let regex = new RegExp("hello", "i");

Common RegEx Methods

Practical Examples

1. Email Validation

Yeh pattern check karta hai ki email ka format (something@something.com) sahi hai ya nahi.

const emailPattern = /^[a-zA-Z0-9._-]+@[a-z]+\.[a-z]{2,4}$/;
console.log(emailPattern.test("test@example.com")); // true
console.log(emailPattern.test("test@example")); // false

2. Mobile Number Validation (10 digits)

Yeh pattern ensure karta hai ki string me sirf 10 digits hi hon.

const phonePattern = /^\d{10}$/;
console.log(phonePattern.test("1234567890")); // true
console.log(phonePattern.test("12345")); // false

Key Takeaways

• RegEx strings me patterns match karne ke liye use hota hai.
• test() method `true` ya `false` return karke pattern existence check karta hai.
• match() method sabhi matches ka array return karta hai.
• replace() method pattern ko nayi value se badalta hai.
• Flags (g, i) search ke behavior ko modify karte hain.