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To check number is a prime number, looping through 2 to your given number-1 and check is any divisible number or not, if have means it’s not a prime number.

Note: 1 is considered neither prime nor composite.

Today, I’m going to show How do I check if the number is a prime number or not in Javascript, here I will create a custom function isPrimeNumber() where I will check if there have any divisible number based on this it will return a boolean value.

Let’s start the today’s tutorial How do you check if the number is prime in JavaScript?

In the following example

  1. check given value is a number
  2. check given value is greater than 1
  3. check given value is prime or not
// function to check if a number is prime or not
function isPrimeNumber(number) {
  // check if the passed value is a number
  if (typeof number == 'number' && !isNaN(number)) {
    if (number > 1) {
      // looping through 2 to number-1
      for (let i = 2; i < number; i++) {
        if (number % i == 0) {
          return false;
      return true;
  return false;


In the above program, we have taken examples of every possible value like parameter if string, number, positive value, a negative value, or NaN values. let’s check the output.

javascript, check if number is prime or not example
javascript, check if number is prime or not example

I hope it’s help you, All the best 👍.