Learn JavaScript
Loops
14.5
Lesson

do...while loop

In the do...while loop, for the first iteration, the code block is executed without any checks. From the second iteration onwards, the statement of the loop is checked at the beginning of the iteration. If the statement evaluates to true, then the code block is run and the loop moves to its next iteration. If the statement evaluates to false, then the loop is immediately terminated and no more code is run.

Let’s look at the example given below, where we print the numbers from 1 to 5 using a do...while loop.

Here, we first initialize a variable i with the value of 1. We then start a do...while loop, the steps for which are as follows:

Step 1 - For the first iteration, the code block is run without any checks, wherein we print the value of i and increment its value by 1. The loop then moves to its second iteration.

Step 2 - At the beginning of the second iteration, the statement i < 6 is checked to see if it evaluates to true. Since, the current value of i is 1, the statement does evaluate to true.

Step 3 - The code block of the loop is then run, where we print the value of i to the console and increment the value of i by 1.

Step 4 - The loop then moves on to the next iteration, wherein it repeats the steps from Step 2.

Steps 2, 3 and 4 are repeated as long as the statement of the do...while loop evaluates to true. At one point, the value of i will be 6 at the beginning of an iteration, due to which the statement i < 6 will evaluate to false. At that point, the loop immediately terminates and no more code is run.

The do while is similar to the while loop, with the only difference being that in the do...while loop, the code block is executed once before checking the condition.