JavaScript While Loop

While Loops execute a block of code as long as a specified condition is true.

---

The while Loop

The while loop loops through a block of code while a specified condition is true.

Syntax

while (variable<endvalue)
  {
  code to be executed
  }

Note: The < could be any comparing operator.

Example

The example below defines a loop that starts with i=0. The loop will continue to run as long as i is less than 5. i will increase by 1 each time the loop runs:

Example

while (i<5)
  {
  x=x + "The number is " + i + "<br />";
  i++;
  }

Try it yourself »

Note: Do not forget to increase the i variable used in the condition, otherwise i will always be less than 5, and the loop will never end!

---

The do...while Loop

The do...while loop is a variant of the while loop. This loop will execute the block of code once, before checking if the condition is true, then it will repeat the loop as long as the condition is true.

Syntax

do
  {
  code to be executed
  }
while (variable<endvalue);

Example

The example below uses a do...while loop. The do...while loop will always be executed at least once, even if the condition is false, because the statements are executed before the condition is tested:

Example

do
  {
  x=x + "The number is " + i + "<br />";
  i++;
  }
while (i<5);

Try it yourself »

Note: Do not forget to increase the i variable used in the condition, otherwise i will always be less than 5, and the loop will never end!