JavaScript For Loops

The for loop is the most commonly used loop in JavaScript. It combines initialization, condition, and increment in one line.

Syntax

for (initialization; condition; increment) {
    // code to repeat
}

Basic Examples

// Count from 1 to 5
for (let i = 1; i <= 5; i++) {
    console.log(i);
}

// Count from 10 to 0
for (let i = 10; i >= 0; i--) {
    console.log(i);
}

// Count by 2s
for (let i = 0; i <= 20; i += 2) {
    console.log(i);  // 0, 2, 4, 6, ... 20
}

Looping Through Arrays

let fruits = ["apple", "banana", "cherry", "date"];

for (let i = 0; i < fruits.length; i++) {
    console.log(`${i + 1}. ${fruits[i]}`);
}
// 1. apple
// 2. banana
// 3. cherry
// 4. date

For...of Loop (Modern)

let colors = ["red", "green", "blue"];

for (let color of colors) {
    console.log(color);
}
// No need to manage an index variable!

For...in Loop (Objects)

let person = { name: "Alice", age: 25, city: "London" };

for (let key in person) {
    console.log(`${key}: ${person[key]}`);
}
// name: Alice
// age: 25
// city: London

Nested Loops

for (let i = 1; i <= 3; i++) {
    for (let j = 1; j <= 3; j++) {
        console.log(`i=${i}, j=${j}`);
    }
}
// Produces 9 combinations