JavaScript Me String Methods & Properties Kya Hote Hain?

String Property: length

The length property string me total kitne characters hain, yeh batata hai (spaces sahit).

let text = "Hello JavaScript";
console.log(text.length); // Output: 16

Common String Methods

1. Accessing Characters

• charAt(index): Ek specific index par maujood character ko return karta hai.
• charCodeAt(index): Ek specific index par maujood character ka Unicode value (ek number) return karta hai.

let text = "JavaScript";
console.log(text.charAt(0)); // Output: "J"
console.log(text.charCodeAt(0)); // Output: 74

2. Extracting String Parts

• slice(start, end): String ka ek hissa extract karta hai. end index include nahi hota. Negative values allow hain.
• substring(start, end): slice jaisa hi hai, lekin negative values ko 0 treat karta hai.
• substr(start, length): start index se `length` characters tak extract karta hai. (Yeh ab deprecated ho chuka hai).

let text = "Hello, World!";
console.log(text.slice(7, 12)); // "World"
console.log(text.substring(0, 5)); // "Hello"

3. Modifying Strings

• replace(searchValue, newValue): String me kisi value ko search karke use nayi value se replace karta hai (sirf pehla match).
• toUpperCase(): Poore string ko uppercase me convert karta hai.
• toLowerCase(): Poore string ko lowercase me convert karta hai.
• concat(str1, str2, ...): Do ya zyada strings ko jodta hai.
• trim(): String ke shuru aur ant se extra spaces hata deta hai.

let greeting = "  Hello World  ";
console.log(greeting.replace("World", "JavaScript")); // "  Hello JavaScript  "
console.log(greeting.toUpperCase()); // "  HELLO WORLD  "
console.log(greeting.trim()); // "Hello World"

4. Searching in Strings

• indexOf(searchValue): Kisi value ka pehla index return karta hai. Agar nahi milta toh -1 return karta hai.
• lastIndexOf(searchValue): Kisi value ka aakhri index return karta hai.
• includes(searchValue): Check karta hai ki string me value hai ya nahi (returns `true` or `false`).
• startsWith(searchValue): Check karta hai ki string kisi specific value se shuru hoti hai ya nahi.
• endsWith(searchValue): Check karta hai ki string kisi specific value par khatm hoti hai ya nahi.

let text = "JavaScript is a powerful language.";
console.log(text.indexOf("powerful")); // 15
console.log(text.includes("Java")); // true
console.log(text.startsWith("Script")); // false

5. Converting String to Array

• split(separator): String ko separator ke basis par tod kar ek array banata hai.

let csv = "apple,banana,mango";
let fruits = csv.split(",");
console.log(fruits); // ["apple", "banana", "mango"]

Key Takeaways

• Strings immutable hote hain, yaani original string change nahi hota, methods ek naya string return karte hain.
• length property string ki total length batati hai.
• slice(), substring() se string ke parts extract kiye jaate hain.
• replace(), toUpperCase(), toLowerCase() se string ko modify kiya jaata hai.
• indexOf(), includes(), startsWith() searching ke liye use hote hain.
• split() string ko array me convert karne ke liye bohot useful hai.