A prime number is a positive integer that is only divisible by **1** and itself. For example, **2**, **3**, **5**, **7**, **11** are the first few prime numbers.

## Example: Check Prime Number

```
// program to check if a number is prime or not
// take input from the user
const number = parseInt(prompt("Enter a positive number: "));
let isPrime = true;
// check if number is equal to 1
if (number === 1) {
console.log("1 is neither prime nor composite number.");
}
// check if number is greater than 1
else if (number > 1) {
// looping through 2 to number-1
for (let i = 2; i < number; i++) {
if (number % i == 0) {
isPrime = false;
break;
}
}
if (isPrime) {
console.log(`${number} is a prime number`);
} else {
console.log(`${number} is a not prime number`);
}
}
// check if number is less than 1
else {
console.log("The number is not a prime number.");
}
```

**Output**

Enter a positive number: 23 23 is a prime number.

In the above program, the user is prompted to enter a number. The number entered by the user is checked if it is greater than **1** using `if...else if... else`

statement.

**1**is considered neither prime nor composite.- All negative numbers are excluded because prime numbers are positive.
- Numbers greater than
**1**are tested using a`for`

loop.

The `for`

loop is used to iterate through the positive numbers to check if the number entered by the user is divisible by positive numbers (**2** to user-entered number minus **1**).

The condition `number % i == 0`

checks if the number is divisible by numbers other than 1 and itself.

- If the remainder value is evaluated to
**0**, that number is not a prime number. - The
`isPrime`variable is used to store a boolean value: either**true**or**false**. - The
`isPrime`variable is set to**false**if the number is not a prime number. - The
`isPrime`variable remains**true**if the number is a prime number.