String Search & Indexing

• indexOf(substring, fromIndex?) → Returns the first occurrence index of a substring (-1 if not found).
• lastIndexOf(substring, fromIndex?) → Returns the last occurrence index of a substring.

let str = "hello world hello";
console.log(str.indexOf("hello"));       // 0 (first occurrence)
console.log(str.indexOf("hello", 5));    // 12 (search after index 5)
console.log(str.lastIndexOf("hello"));   // 12 (last occurrence)

• includes(substring) → Checks if a string contains a substring.

console.log("hello".includes("ll")); // true

• startsWith(searchString) / endsWith(searchString) → Checks if a string starts or ends with a substring.

console.log("hello".startsWith("he")); // true
console.log("hello.js".endsWith(".js")); // true

Extracting & Modifying Strings

• charAt(index) → Returns the character at a specific index.

let str = "Hello";
console.log(str.charAt(1)); // "e"

• substring(start, end?) → Extracts part of a string (swaps start and end if start > end).

console.log("JavaScript".substring(4, 10)); // "Script"
console.log("JavaScript".substring(10, 4)); // "Script" (arguments swapped)

• slice(start, end?) → Extracts part of a string (supports negative indexes).

console.log("JavaScript".slice(-6)); // "Script"
console.log("JavaScript".slice(10, 4)); // "" (empty, as arguments are not swapped)

• split(separator, limit?) → Splits a string into an array based on a separator.

let str = "apple,banana,grape";
console.log(str.split(",")); // ["apple", "banana", "grape"]

Case Transformation

• toLowerCase() → Converts the string to lowercase.
• toUpperCase() → Converts the string to uppercase.