A program for the Recurse Center application

emirpChecker.js

/* 
If a prime is still prime when you reverse the digits 
and it is a different prime, then it is an emirp.
https://en.wikipedia.org/wiki/Emirp
The sequence begins with 13 and 2,3,5,7,11 
should not return as emirp because they are palindromes. 
*/

function isNotNum(num) {
  return /[^0-9]/.test(String(num));
}

function isPrime(num) {
  /* Starts at 2 because all numbers are divisible by 1. 
          It runs until i <  num because all primes are 
          divisible by themselves. */
  for (let i = 2; i < num; i++) {
    /*if the number is divisible by any number 
          other than itself  and one it is not prime */
    if (num % i === 0) {
      return false;
    }
  }
  /*  0 and 1 are not prime */
  return num > 1;
}

function isEmirp(num) {
  const reversePrime = parseInt(num.toString().split("").reverse().join(""));

  if (!isPrime(num) || isNotNum(num)) {
    console.log(`${num} is not a prime`);
  } else if (isPrime(reversePrime) && reversePrime !== num) {
    console.log(`${num} is an emirp (reverse is ${reversePrime})`);
  } else {
    console.log(`${num} is prime but not an emirp`);
  }
}