How to check if a number is prime in JavaScript

A prime number is a number that should be greater than 1 and divisible by 1 and itself only. Prime numbers are beneficial in secure digital communication, play a vital role in encryption, and act as a building block in solving various mathematical and programming problems.

Goal

In this Answer, our goal is to find whether a given number is prime or not as illustrated in the given table below.

Prime numbers are mostly odd numbers except 2, which is the only even prime number. Both 2 and 3 are the only two consecutive integers prime in number counting.

Code example

There are multiple ways to solve this problem, but we’ll use the following approach to check $N$ is prime or not:

Check if $N$ divisible by any number from $2$ up to $n / 2$ .
Check the reminder of each number upto $n/2$ .
If reminder of all the numbers upto $n/2$ is zero, then number is not prime. Otherwise, it is prime.

//Prime number is implementation
function checkPrime (n) {
    
    if (n <= 1)
    {
        return false;
    }
    else
    {
       let m=2;
       while(m <= n/2)
       {
           if((n%m) == 0)
           {
              return  false;
           }
           m++;
              
       }
       return true;
    }
}
//check if the number is prime
console.log(checkPrime(2));  //true
console.log(checkPrime(3));  //true
console.log(checkPrime(4));  //false
console.log(checkPrime(5));  //true
console.log(checkPrime(7));  //true
console.log(checkPrime(8));  //false
console.log(checkPrime(11)); //true

Explanation

Let’s discuss the code above in detail.

Line 2: Define the checkPrime function that takes n as an input parameter.
Lines 4–6: Check if a n is less than or equal to 1. If the condition is true, we return false value as it is not a prime number. Otherwise, the else statement will execute.
Lines 8–15: Use the for loop to check reminders of each number from 2 to upto n/2. If the n is divisible by all numbers, then it is not prime, return false (e.g., for input number 4). Otherwise, it returns true.

As we’ve seen in this Answer, determining whether a number is prime is a straightforward task in JavaScript. This foundational skill allows for confidently and easily exploring diverse applications and problem-solving scenarios.

If you want to learn this task in different languages such as C++, Python, Java, or Dart. Please visit the following Answers on our platform:

Number	Divisible By	Prime?
2	1,2	Yes
3	1,3	Yes
4	1,2,4	No
5	1,5	Yes
6	1,2,3,6	No
7	1,7	Yes