In this tutorial, we will learn how to write a simple JavaScript program to determine whether a given number is a prime number. We will use a simple looping mechanism and the modulo operator to achieve this. By the end of this tutorial, you will have a solid understanding of how to write a prime number checker in JavaScript.

What is a Prime Number?

A prime number is a natural number greater than 1 that is not a product of two smaller natural numbers. In other words, it is a number divisible only by 1 and itself. For example, the first six prime numbers are 2, 3, 5, 7, 11, and 13.

Why Check Prime Numbers with JavaScript?

JavaScript is a versatile and powerful programming language that can be used for many applications. It is well-suited for use in web development and can be used to create dynamic and interactive user interfaces. With its growing popularity and widespread use, JavaScript is an excellent choice for those looking to learn to code or develop web applications.

In addition to its versatility, JavaScript is relatively easy to learn and use, making it an ideal choice for those looking to check if a number is a prime quickly.

How to Check Prime Numbers with JavaScript

There are several methods for checking if a number is prime or not using JavaScript, but we’ll discuss the most straightforward and efficient one.

Here’s the code for our JavaScript program to check prime numbers:

					function isPrime(num) {
  if (num < 2) return false;
  for (let i = 2; i < num; i++) {
    if (num % i === 0) {
      return false;
  return true;


Let’s break down this code and see how it works.

The first line of the code defines the function isPrime(num), which takes a number as an input and returns a Boolean value indicating whether or not the number is prime.

The second line checks if the number is less than or equal to 1. If it is, the function returns false because 1 is not a prime number.

The next section of the code uses a for loop to check if the number is divisible by any smaller numbers. The loop starts at 2 and continues until i is less than the tested number. If the number is divisible by any of these smaller numbers, the function returns false because the number is not prime.

If the number is not divisible by any smaller numbers, the function returns true, indicating that the number is prime.

Putting it All Together

Now that we’ve discussed the code for our JavaScript program to check prime numbers, let’s see it in action. First, here’s an example of how to use the isPrime function to check if a number is prime:

					const num = 7;
console.log(`Is ${num} a prime number? ${isPrime(num)}`);


This code sets the variable num to 7 and then uses the console.log function to display the result of calling the isPrime function with num as its argument. The output should be Is 7 a prime number? true.

Understanding the basics of how to check for a prime number using JavaScript is an essential part of any JavaScript programmer’s skill set. This can be a simple but essential step in solving various mathematical problems in your coding projects. With the use of loops, conditional statements and the modulo operator, you can quickly determine if a number is prime. It is also important to note that prime numbers play a crucial role in various areas of mathematics and cryptography, making them a fundamental aspect of modern technology.

Thanks for reading. Happy coding!