# 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

- Declare a variable
`i`

and initialize it to 1. - 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

- Declare variables
`n`

and`sum`

. - Assign a value to
`n`

. - Initialize
`sum`

to 0. - Use a while loop to calculate the sum of the first
`n`

natural numbers. - 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

- Declare variables
`num`

and`rev`

. - Assign a value to
`num`

. - Initialize
`rev`

to 0. - Use a while loop to reverse the digits of
`num`

. - 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