For whom is this code challenge ?

  • People preparing for coding interviews or willing to improve their coding skills.

What material can I use when completing this challenge ?

  • Computer without an internet connection.

Is there a time limit ?

  • No time limit for this challenge.

What is the difficuly of this challenge ?

  • This challenge is designed for beginners.

What programming language can I use ?

  • Any programming language can be used to complete this challenge. The only restriction is to not use any existing functions or libraries in the solution.


Given a number x, write a function isPrime(x) which returns true where x is a prime number otherwise false.

Note : A prime number is an integer greater than 1 which can be divided without remainder, only by 1 and itself, see examples below in section Output


1) isPrime(1) is false

2) isPrime(2) is true

3) isPrime(3) is true

4) isPrime(4) is false

5) isPrime(5) is true


Note : Readers willing to answer this coding question by themselves should stop reading here. Below this point, the solution will be discussed and the answer will be provided.

The method used to check if a number x is prime is to divide it successively by all the numbers between 2 and x - 1 and verify that those divisions have a remainder. If this is the case then x is prime, otherwise not. Find below the code for the function isPrime(x).

The below code is complete and can be run on your machine by copying and pasting it in your coding environment. To reproduce the outputs from the section Output run the entire code below with a JavaScript interpreter (e.g. NodeJS), the results will be displayed in the output console.


function isPrime(x) {
    if (x <= 1) return false
    for (let i = 2 ; i < x ; i++) if (x % i == 0) return false
    return true