While Loop in JavaScript

In this tutorial, we will learn about while loops in JavaScript. We will cover the basics of iterative execution using while loops.

What is a While Loop

A while loop is a control flow statement that allows code to be executed repeatedly based on a given Boolean condition. The loop runs as long as the condition evaluates to true.

Syntax

The syntax for the while loop in JavaScript is:

while (condition) {
    // Code block to be executed
}

The while loop evaluates the condition before executing the loop's body. If the condition is true, the code block inside the loop is executed. This process repeats until the condition becomes false.


Example 1: Printing Numbers from 1 to 5

  1. Declare a variable i and initialize it to 1.
  2. Use a while loop to print numbers from 1 to 5.

JavaScript Program

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

Output

1
2
3
4
5

Example 2: Calculating the Sum of First N Natural Numbers

  1. Declare variables n and sum.
  2. Assign a value to n.
  3. Initialize sum to 0.
  4. Use a while loop to calculate the sum of the first n natural numbers.
  5. Print the sum.

JavaScript Program

let n = 10;
let sum = 0;
let i = 1;
while (i <= n) {
    sum += i;
    i++;
}
console.log(`Sum of first ${n} natural numbers is ${sum}`);

Output

Sum of first 10 natural numbers is 55

Example 3: Reversing a Number

  1. Declare variables num and rev.
  2. Assign a value to num.
  3. Initialize rev to 0.
  4. Use a while loop to reverse the digits of num.
  5. Print the reversed number.

JavaScript Program

let num = 12345;
let rev = 0;
while (num !== 0) {
    let digit = num % 10;
    rev = rev * 10 + digit;
    num = Math.floor(num / 10);
}
console.log(`Reversed number is ${rev}`);

Output

Reversed number is 54321