Find the prime factors of a number in JavaScript

The prime factors of a number are the prime numbers that divide the number exactly. An easy way to find the prime factors of a number is using trial division, which is a simple algorithm that checks each possible prime factor in order.

[!WARNING]

This algorithm is not efficient for large numbers, as it has a high time complexity. You should look into more efficient algorithms for prime factorization, if you plan to implement this in a production environment.

Implementing the algorithm is straightforward. You can use a while loop to iterate over all possible prime factors, starting with 2. If the current factor, f, exactly divides n, add f to the factors array and divide n by f. Otherwise, increment f by one.

const primeFactors = n => {
  let a = [],
    f = 2;
  while (n > 1) {
    if (n % f === 0) {
      a.push(f);
      n /= f;
    } else {
      f++;
    }
  }
  return a;
};

primeFactors(147); // [3, 7, 7]