JavaScript while Statement
Example
Loop through a block of code as long as a variable (i) is less than 5:
var text = "";
var i = 0;
while (i < 5) {
text += "<br>The number is " + i;
i++;
}
Try it Yourself »
More "Try it Yourself" examples below.
Definition and Usage
The while statement creates a loop that is executed while a specified condition is true.
The loop will continue to run as long as the condition is true. It will only stop when the condition becomes false.
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
- for/of - loops through the values of an iterable 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
Tip: Use the break statement to break out of a loop, and the continue statement to skip a value in the loop.
Browser Support
| Statement | |||||
|---|---|---|---|---|---|
| while | Yes | Yes | Yes | Yes | Yes |
Syntax
while (condition) {
code block to be executed
}
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. |
Technical Details
| JavaScript Version: | ECMAScript 1 |
|---|
More Examples
Example
Loop through the indices of an array to collect the car names from the cars array:
var cars = ["BMW", "Volvo", "Saab", "Ford"];
var text = "";
var i = 0;
while (i < cars.length) {
text += cars[i] + "<br>";
i++;
}
Try it Yourself »
Example above explained:
- First, we set a variable before the loop starts (var i = 0;)
- Then, we define the condition for the loop to run. As long as the variable is less than the length of the array (which is 4), the loop will continue
- Each time the loop executes, the variable is incremented by one (i++)
- Once the variable is no longer less than 4 (array's length), the condition is false, and the loop will end
Example
Loop backwards through the indices of an array:
var cars = ["BMW", "Volvo", "Saab", "Ford"];
var text = "";
var len = cars.length;
while (len--) {
text += cars[len] + "<br>";
}
Try it Yourself »
Example
Using the break statement - Loop through a block of code, but exit the loop when the variable i is equal to "3":
var text = "";
var i = 0;
while (i < 5) {
text += "<br>The number is " + i;
i++;
if (i == 3) {
break;
}
}
Try it Yourself »
Example
Using the continue statement - Loop through a block of code, but skip the value of "3":
var text = "";
var i = 0;
while (i < 5) {
i++;
if (i == 3) {
continue;
}
text += "<br>The number is " + i;
}
Try it Yourself »
Related Pages
JavaScript Tutorial: JavaScript While Loop
JavaScript Reference: JavaScript do ... while Statement
JavaScript Reference: JavaScript for Statement
JavaScript Reference: JavaScript break Statement
JavaScript Reference: JavaScript continue Statement
