kata-6-solution-backwards-read-primes.js

// ************************************************************************************
// https://www.codewars.com/kata/5539fecef69c483c5a000015/javascript

// Find all Backwards Read Primes between two positive given numbers (both inclusive), 
// the second one always being greater than or equal to the first one. 
//The resulting array or the resulting string will be ordered following the natural order 
// of the prime numbers.

// Example
// backwardsPrime(2, 100) => [13, 17, 31, 37, 71, 73, 79, 97] 
// backwardsPrime(9900, 10000) => [9923, 9931, 9941, 9967] 
// backwardsPrime(501, 599) => []
// ************************************************************************************

function backwardsPrime(start, stop) {
  // your code here
  let result = [];
  for (let i = start; i <= stop; i++) {
    // check if the number is prime
    // if it is prime check if the backwards no is prime too
    if (isPrime(i) && isReversePrime(i)) {
      result.push(i);
    }
  }
  return result;
}

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

function isReversePrime(num) {
  let reverseNum = +num.toString().split("").reverse().join("");
  if (num !== reverseNum) {
    return isPrime(reverseNum);
  }
  return false;
}

Greate job!!!