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目录

JavaScript while Loop

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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 i for 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:

The JavaScript while Tutorial

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
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