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while

The while statement creates a loop that executes a specified statement as long as the test condition evaluates to true. The condition is evaluated before executing the statement.

Syntax

while (condition)
  statement
condition
An expression evaluated before each pass through the loop. If this condition evaluates to true, statement is executed. When condition evaluates to false, execution continues with the statement after the while loop.
statement
An optional statement that is executed as long as the condition evaluates to true. To execute multiple statements within the loop, use a block statement ({ ... }) to group those statements.

Note: Use the break statement to stop a loop before condition evaluates to true.

Examples

Using while

The following while loop iterates as long as n is less than three.

var n = 0;
var x = 0;

while (n < 3) {
  n++;
  x += n;
}

Each iteration, the loop increments n and adds it to x. Therefore, x and n take on the following values:

  • After the first pass: n = 1 and x = 1
  • After the second pass: n = 2 and x = 3
  • After the third pass: n = 3 and x = 6

After completing the third pass, the condition n < 3 is no longer true, so the loop terminates.

Specifications

Browser compatibilityUpdate compatibility data on GitHub

Desktop
Chrome Edge Firefox Internet Explorer Opera Safari
while 1 12 1 3 3 1
Mobile
Android webview Chrome for Android Firefox for Android Opera for Android Safari on iOS Samsung Internet
while 1 18 4 10.1 1 1.0
Server
Node.js
while 0.1.100

See also

© 2005–2018 Mozilla Developer Network and individual contributors.
Licensed under the Creative Commons Attribution-ShareAlike License v2.5 or later.
https://wiki.developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Statements/while