Eratosthenes to the rescue in finding prime factors of a given number

AllPrimeFactorsOfN.js

function primeFactorsOf(n) {
  var lpfs = leastPrimeFactorsOf(n);
  return helper(lpfs, n, []);
  function helper(lpfs, n, arra) {
    if (lpfs[n] == 0) return arra.concat([n]);
    return helper(lpfs, n/lpfs[n], arra.concat([lpfs[n]]));
  }
}

function leastPrimeFactorsOf(n) {
  var sieve = new Array(n + 1).fill(0);
  for (var i = 2; i <= Math.ceil(Math.sqrt(n)); i++) {
    for (var j = 2; j <= n; j++) {
      if (j > i && j % i === 0 && sieve[j] === 0) sieve[j] = i;
    }
  }
  return sieve;
}

primeFactorsOf(4212234)
> [2, 3, 3, 13, 47, 383]

primeFactorsOf(42122344)

...still thinking about it