Comparing while and do-while Loops in JavaScript

In the previous article, we explored the while loop in JavaScript and its benefits for repetitive tasks. Now, let’s dive into another type of loop: the do-while loop.

Although both loops serve similar purposes, they have distinct characteristics that make them suitable for different scenarios. In this article, we’ll compare the while and do-while loops and highlight their important differences.

The while loop recap

Just to refresh your memory, the while loop executes a block of code repeatedly as long as a specified condition evaluates to true. Here’s a quick example that counts from 1 to 5:

let count = 1;

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

Introducing the do-while loop

The do-while loop is quite similar to the while loop, but with one key difference: the condition is checked after the loop body is executed. This means that the loop body will always run at least once, even if the condition is initially false.

Here’s the basic syntax of a do-while loop:

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

Comparing the Loops

Let’s compare the while and do-while loops using an example. Imagine you’re asking a user for a number greater than 10, and you want to keep asking until they provide valid input.

Using a while Loop:

let userInput;

while (userInput <= 10) {
  userInput = parseInt(prompt("Enter a number greater than 10:"));
}

In this while loop, the loop condition is checked before the loop body executes. This means that if the initial input is 12 (greater than 10), the loop won’t execute at all.

Using a do-while Loop:

let userInput;

do {
  userInput = parseInt(prompt("Enter a number greater than 10:"));
} while (userInput <= 10);

With the do-while loop, the loop body executes first, and then the condition is checked. This guarantees that the user is prompted at least once, ensuring they provide an input.

Key Differences and Use Cases

  1. Initial Execution: As seen in the examples, the while loop might not execute at all if the condition is false from the start, while the do-while loop always runs at least once.

  2. Input Validation: The do-while loop is handy for input validation scenarios, ensuring that users provide valid inputs before the loop exits.

  3. General Repetition: Use the while loop when you need to repeat a block of code while a certain condition is met. Use the do-while loop when you want to ensure that the code block executes at least once.