Loops: for, while, do...while

Syntax

for (init; condition; step) { }
while (condition) { }
do { } while (condition);

Examples

for (let i = 0; i < 5; i++) {
  console.log(i); // 0, 1, 2, 3, 4
}

// Looping over an array by index
const fruits = ["apple", "banana", "cherry"];
for (let i = 0; i < fruits.length; i++) {
  console.log(fruits[i]);
}

let count = 0;
while (count < 3) {
  console.log(count);
  count++;
}
// 0, 1, 2

let attempts = 0;
do {
  console.log(`Attempt ${attempts + 1}`);
  attempts++;
} while (attempts < 3);

// Runs at least once even if the condition starts false
let x = 10;
do {
  console.log("This runs once even though x is not < 5");
} while (x < 5);

Best practices

• Use for...of instead of a classic for loop when you just need each value, not the index
• Use while when the number of iterations is not known ahead of time and depends on a changing condition
• Use do...while specifically when the loop body must run at least once regardless of the condition
• Always ensure the loop condition will eventually become false, to avoid accidental infinite loops

At a glance

Purpose

Application logic and interaction

File extension

.js · .mjs

Runs in

Browsers and JavaScript runtimes

Usually used with

HTML, CSS and Web APIs

Specifications & further reading

• ECMAScript specification

Related JavaScript documentation