JavaScript Strings

Strings are sequences of characters used to represent text. They are one of the most commonly used data types.

Creating Strings

let single = 'Hello';
let double = "Hello";
let backtick = `Hello`;  // Template literal

// All three create a string
console.log(typeof single);  // "string"

Template Literals

let name = "Alice";
let age = 25;

// Old way — concatenation
let msg1 = "My name is " + name + " and I'm " + age;

// Modern way — template literals
let msg2 = `My name is ${name} and I'm ${age}`;

// Multi-line strings
let multiLine = `
    This is line 1
    This is line 2
    This is line 3
`;

String Properties and Methods

let str = "Hello, World!";

str.length;              // 13
str.toUpperCase();       // "HELLO, WORLD!"
str.toLowerCase();       // "hello, world!"
str.trim();              // Remove whitespace from both ends
str.indexOf("World");    // 7 (position of first match)
str.includes("Hello");   // true
str.startsWith("Hello"); // true
str.endsWith("!");       // true
str.replace("World", "JavaScript"); // "Hello, JavaScript!"
str.charAt(0);           // "H"
str[0];                  // "H" (bracket notation)

String Immutability

let str = "Hello";
str[0] = "h";         // Doesn't work — strings are immutable
console.log(str);      // "Hello" (unchanged)

// Create a new string instead
let newStr = "h" + str.slice(1);
console.log(newStr);   // "hello"