JavaScript while Loop
Example
Loop a code block as long as a i is less than 5:
let text = "";
let i = 0;
while (i < 5) {
text += i + "<br>";
i++;
}
Try it Yourself »
Loop (iterate over) an array to collect car names:
const cars = ["BMW", "Volvo", "Saab", "Ford"];
let text = "";
let i = 0;
while (i < cars.length) {
text += cars[i] + "<br>";
i++;
}
Try it Yourself »
- The loop starts in position 0 (
let i = 0). - The loop increments
ifor each run (i++). - The loop runs as long as
i < cars.length.
More examples below.
Description
The while statement creates a loop (araund a code block) that is executed while a condition is
true.
The loop runs while the condition is true. Otherwise it stops.
See Also:
JavaScript Loop Statements
| Statement | Description | |
| break | Breaks out of a loop | |
| continue | Skips a value in a loop | |
| while | Loops a code block while a condition is true | |
| do...while | Loops a code block once, and then while a condition is true | |
| for | Loops a code block while a condition is true | |
| for...of | Loops the values of any iterable | |
| for...in | Loops the properties of an object |
Syntax
while (condition) {
code block to be executed
}
Parameters
| Parameter | Description |
| condition | Required. The condition for running the code block. If it returns true, the code clock will start over again, otherwise it ends. |
Note
If the condition is always true, the loop will never end. This will crash your browser.
If you use a variable in the condition, you must initialize it before the loop, and increment it within the loop. Otherwise the loop will never end. This will also crash your browser.
More Examples
Loop over an array in descending order (negative increment):
const cars = ["BMW", "Volvo", "Saab", "Ford"];
let text = "";
let len = cars.length;
while (len--) {
text += cars[len] + "<br>";
}
Try it Yourself »
Using break - Loop through a block of code, but exit the loop when i == 3:
let text = "";
let i = 0;
while (i < 5) {
text += i + "<br>";
i++;
if (i == 3) break;
}
Try it Yourself »
Using continue - Loop through a block of code, but skip the value 3:
let text = "";
let i = 0;
while (i < 5) {
i++;
if (i == 3) continue;
text += i + "<br>";
}
Try it Yourself »
Browser Support
while is an ECMAScript1 (ES1) feature.
ES1 (JavaScript 1997) is fully supported in all browsers:
| Chrome | Edge | Firefox | Safari | Opera | IE |
| Yes | Yes | Yes | Yes | Yes | Yes |