PersistentBugger.js

/**
 * Description:
 *
 * Write a function, persistence, that takes in a
 * positive parameter num and returns its
 * multiplicative persistence, which is the number
 * of times you must multiply the digits in
 * num until you reach a single digit.
 *
 * For example (Input --> Output):
 *
 * 39 --> 3 (because 3*9 = 27, 2*7 = 14, 1*4 = 4 and 4 has only one digit)
 * 999 --> 4 (because 9*9*9 = 729, 7*2*9 = 126, 1*2*6 = 12, and finally 1*2 = 2)
 * 4 --> 0 (because 4 is already a one-digit number)
 *
 * Kata URL: https://www.codewars.com/kata/55bf01e5a717a0d57e0000ec
 *
 * @param {*} num
 * @returns
 */

function persistence(num) {
  let result = 0;
  let numbers = (num + "").split("");

  while (numbers.length > 1) {
    let subtotal = 1;
    numbers.forEach((element) => {
      subtotal *= parseInt(element);
    });
    numbers = (subtotal + "").split("");
    result++;
  }
  return result;
}