JavaScript do…while Loop

A do…while loop in JavaScript is a control structure where the code executes repeatedly based on a given boolean condition. It’s similar to a repeating if statement. One key difference is that a do…while loop guarantees that the code block will execute at least once, regardless of whether the condition is met initially or not.

There are mainly two types of loops.

• Entry Controlled loops: In this type of loop, the test condition is tested before entering the loop body. For Loop and While Loops are entry-controlled loops.
• Exit Controlled Loops: In this type of loop the test condition is tested or evaluated at the end of the loop body. Therefore, the loop body will execute at least once, irrespective of whether the test condition is true or false. the do-while loop is exit controlled loop.

Syntax:

do {
    // Statements
}
while(conditions)

Example 1: In this example, we will illustrate the use of a do…while loop

let test = 1;
do {
    console.log(test);
    test++;
} while(test<=5)

Output:

1
2
3
4
5

The main difference between do…while and while loop is that it is guaranteed that do…while loop will run at least once. Whereas, the while loop will not run even once if the given condition is not satisfied

Example 2: In this example, we will try to understand the difference between the two loops

let test = 1;
do {
    console.log(test);
} while(test<1)

while(test<1){
    console.log(test);
}

Output:

1

Explanation: We can see that even if the condition is not satisfied in the do…while loop the code still runs once, but in the case of while loop, first the condition is checked before entering into the loop. Since the condition does not match therefore the while loop is not executed.

Let us compare the while and do…while loop

Note: When we are writing conditions for the loop we should always add a code that terminates the code execution otherwise the loop will always be true and the browser will crash.

Supported Browser:

• Chrome
• Edge
• Safari
• Firefox
• Internet Explorer

We prefer you to check this article to know more about JavaScript Loop Statements.

JavaScript do…while Loop – FAQs

What is a do…while loop in JavaScript?

A do…while loop is a control flow statement that allows code to be executed repeatedly based on a given Boolean condition. Unlike a regular while loop, a do…while loop will execute the code block once before checking the condition.

What is the basic syntax of a do…while loop?

The basic syntax of a do…while loop includes the do keyword followed by a code block in curly braces and the while keyword followed by a condition in parentheses.

How does the do…while loop work?

The do…while loop first executes the code block once, and then evaluates the condition. If the condition is true, the loop repeats, executing the code block again. This process continues until the condition evaluates to false.

What is the difference between while and do…while loops?

• while loop: Checks the condition before executing the code block. If the condition is false initially, the code block may never execute.
• do…while loop: Executes the code block once before checking the condition. This guarantees that the code block will execute at least once, even if the condition is false initially.

How do you break out of a do…while loop early?

You can use the break statement to exit a do…while loop before it completes all its iterations. This is useful if you want to stop the loop based on a condition inside the loop body.

How do you skip an iteration in a do…while loop?

You can use the continue statement to skip the current iteration and proceed to the next iteration of the loop. This is useful if you want to skip certain iterations based on a condition.

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Article Tags :

• JavaScript
• Web Technologies
• javascript-basics
• Loops & Control Structure