JavaScript implementation of finding prime numbers code sharing_javascript skills

Okay, there is no background explanation, no advanced skills, just boring, I want to find all the prime numbers within 10,000. So here we go:

function zhishu(num) {
  if (num == 1) {
    return false;
  }
  if (num == 2) {
    return true;
  }
  for (var i = 2; i <= Math.sqrt(num); i++) {
    if (num % i == 0) {
      return false;
    }
  }
  return true;
}

Usage examples:

var zhishuArray = [];
for (var j = 1; j < 100000; j++) {
  if (zhishu(j)) {
    zhishuArray.push(j);
  }
}
console.dir(zhishuArray);