JavaScript do...while Loop (original) (raw)

Last Updated : 30 Jul, 2024

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

JavaScript `

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

JavaScript `

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.