nthPrimeNumber.js

function nthPrimeNumber(num) {
  var primes = [0, 0, 2];
  var max = Math.pow(10, 4);
  for (var i=3; i < max + 1; i++) {
    if (i % 2 == 0) {
      primes.push(0);
    } else {
      primes.push(i);
    }
  }

  var j = 3
  while (true) {
    // sieve
    for (var k = j*j; k < primes.length; k += j) {
      primes[k] = 0;
    }

    // finding the next item bigger than j to use for sieve
    for (var x = j; x < primes.length; x += 1) {
      if (primes[x] > j) {
        j = x;
        break;
      }
    }

    // break condition
    if (j*j > primes.length) {
      break;
    }
  }

  // gives back the primes array without zeros
  primes = primes.filter(function(x){if (x > 0) {return x;}});
  return primes[num - 1];
}