A simple JavaScript function that does prime factorization

Question

This is a simple JavaScript function that does prime factorization.

I wrote it on an Android phone with online editor (I don't have access to computers in night time):

Code:

function factorize(n) {
  if (!(Number.isInteger(n) && n >= 2)) {
    throw 'Input is invalid'
  }
  const factors = []
  while (n % 2 == 0) {
    factors.push(2)
    n /= 2
  }
  for (let i=3; i<=Math.round(Math.sqrt(n)+1); i+=2) {
    while (n % i == 0) {
      factors.push(i)
      n /= i
    }
  }
  if (n > 1) {
    factors.push(n)
  }
  return factors
}

console.log(factorize(31556952))

Output

> Array [2, 2, 2, 3, 3, 3, 3, 3, 3, 7, 773]

The test number is the number of seconds in a Gregorian year.

How can it be improved?

Answer 1

Taking a square root is a very slow operation, so it's a bad idea to do it for every iteration of the loop. Rather, you should only update the limit whenever n changes.