JavaScript while

while keeps running its body for as long as the condition is true. Unlike for, there’s no counter built into the syntax — you manage the state yourself.

let i = 0;

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

This is equivalent to for (let i = 0; i < 3; i++) { … }. Use while when “until something happens” reads better than counting.

let dice;
let rolls = 0;

while (dice !== 6) {
  dice = Math.floor(Math.random() * 6) + 1;
  rolls++;
}

console.log(`Got a 6 after ${rolls} rolls`);

do..while — Run At Least Once

do..while checks the condition AFTER the body. The body runs at least once.

let n = 10;

do {
  console.log(n);
  n--;
} while (n > 0);
// 10, 9, 8, ..., 1

do..while is rare — useful when “we want to ask the user at least once” patterns. For most loops, plain while is fine.

Avoiding Infinite Loops

A while loop forgets the condition is your responsibility. If nothing inside the body ever makes the condition false, you have an infinite loop.

let n = 0;
while (n < 10) {
  console.log(n);
  // Forgot n++ — n stays at 0 forever
}

If your tab freezes, this pattern is the usual culprit. Modern browsers will eventually offer to kill the page, but you’ll lose unsaved state.

When to Use Each Loop

Up Next

Two keywords that change the flow inside any loop — break and continue.