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What is a do...while loop in JavaScript

A do...while loop in JavaScript is a variant of the while loop. It is used to execute a block of code at least once, and then repeatedly execute the loop as long as a specified condition is true. The key difference between a while loop and a do...while loop is when the condition is checked: a while loop checks the condition before the code within the loop is executed, whereas a do...while loop checks the condition after the code within the loop has executed. This ensures that the code inside the do...while loop runs at least once, even if the condition is false on the first check.

Syntax

The syntax of a do...while loop is:

do {
  // code block to be executed
} while (condition);

• condition: This is a boolean expression that is evaluated after each iteration of the loop. If the condition evaluates to true, the loop will continue to execute. If it evaluates to false, the loop terminates, and the program continues with the next statement after the loop.

Example

Here's an example that demonstrates the use of a do...while loop, printing numbers 1 to 5:

let i = 1;

do {
  console.log(i);
  i++;
} while (i <= 5);

In this example:

• The loop starts by executing the code block inside the do statement, printing the current value of i to the console and then incrementing i.
• After the code block is executed, the condition (i <= 5) is checked. If it's true, the loop executes again. If it's false, the loop stops.
• This ensures that the code block inside the do...while loop is executed at least once.

Key Points

• The do...while loop is particularly useful when the code block inside the loop needs to be executed at least once, regardless of whether the condition is initially true or false.
• Just like with while loops, it's important to ensure that the condition will eventually become false. Otherwise, you may create an infinite loop, which can freeze or crash your program.
• The condition in a do...while loop is checked after the code block has executed, making it the defining characteristic that differentiates it from the while loop.

Usage

• Use a do...while loop when you need to ensure that the loop's code block is executed at least once.
• Though not as commonly used as the for loop or the while loop, the do...while loop has its specific use cases, especially in scenarios where the initial condition might not be met but an initial execution of the loop's body is required for setting up conditions or performing tasks that are necessary before any conditional check.