JavaScript do/while Statement

Example

This loop will always be executed at least once, even if the condition is false, because the code block is executed before the condition is tested:

var text = "";
var i = 0;
do {
text += "The number is " + i;
i++;
}
while (i < 5);

The result of text will be:

The number is 0
The number is 1
The number is 2
The number is 3
The number is 4

Try it Yourself »

Definition and Usage

The do/while statement creates a loop that executes a block of code once, before checking if the condition is true, then it will repeat the loop as long as the condition is true.

The do/while statement is used when you want to run a loop at least one time, no matter what.

JavaScript supports different kinds of loops:

for - loops through a block of code a number of times
for/in - loops through the properties of an object
while - loops through a block of code while a specified condition is true
do/while - loops through a block of code once, and then repeats the loop while a specified condition is true

Browser Support

The numbers in the table specify the first browser version that fully supports the statement.

Statement
do/while	Yes	6.0	Yes	Yes	Yes

Syntax

do {
code block to be executed
}
while (condition);

Parameter Values

Parameter	Description
condition	Required. Defines the condition for running the loop (the code block). If it returns true, the loop will start over again, if it returns false, the loop will end. Note: If the condition is always true, the loop will never end. This will crash your browser. Note: If you are using a variable with the condition, initialize it before the loop, and increment it within the loop. If you forget to increase the variable, the loop will never end. This will also crash your browser.

Parameter

Description

condition

Required. Defines the condition for running the loop (the code block). If it returns true, the loop will start over again, if it returns false, the loop will end.

Note: If the condition is always true, the loop will never end. This will crash your browser.

Note: If you are using a variable with the condition, initialize it before the loop, and increment it within the loop. If you forget to increase the variable, the loop will never end. This will also crash your browser.