Strings

Strings

What it means

Strings represent text. JavaScript strings are immutable (can’t be changed, only replaced) and support both single quotes, double quotes, and template literals (backticks) for interpolation.

Examples

// String creation
const name1 = "Alice";
const name2 = 'Bob';
const greeting = `Hello, ${name1}!`; // template literal

// String properties
console.log(name1.length); // 5

// Common methods
const text = "  JavaScript  ";
console.log(text.trim());              // "JavaScript"
console.log(text.toLowerCase());       // "  javascript  "
console.log(text.toUpperCase());       // "  JAVASCRIPT  "

const sentence = "Hello World";
console.log(sentence.split(" "));      // ["Hello", "World"]
console.log(sentence.includes("World")); // true
console.log(sentence.startsWith("Hello")); // true
console.log(sentence.endsWith("World"));   // true
console.log(sentence.indexOf("World"));    // 6
console.log(sentence.slice(0, 5));         // "Hello"
console.log(sentence.substring(6));        // "World"
console.log(sentence.replace("World", "JS")); // "Hello JS"

// Template literals
const name = "Alice";
const age = 25;
const bio = `
  Name: ${name}
  Age: ${age}
  Status: ${age >= 18 ? "Adult" : "Minor"}
`;

// String repeat and pad
console.log("*".repeat(5));            // "*****"
console.log("5".padStart(3, "0"));     // "005"
console.log("5".padEnd(3, "0"));       // "500"

Common mistake

Trying to mutate strings directly:

// BAD - strings are immutable
let text = "hello";
text[0] = "H"; // Doesn't work! text is still "hello"

// GOOD - create new string
text = "H" + text.slice(1); // "Hello"
// or
text = text.replace("h", "H"); // "Hello"

Fix: Always create new strings instead of trying to modify existing ones.

Quick practice

1. How do you combine (concatenate) two strings?

   Answer

   `str1 + str2` or use template literal: `` `${str1}${str2}` ``

2. What does "hello".split("") return?

   Answer

   `["h", "e", "l", "l", "o"]` - splits into individual characters

3. Convert ” HELLO ” to “hello” (trimmed and lowercase).

   Answer

   `" HELLO ".trim().toLowerCase()`