function persistence(num) {
  let product = num
  let count = 0
  const splitNumArray = (product) => {
    return product.toString().split("").map(int => Number(int)).reduce((a, b) => a*b)
  }
  while (product >= 10) {
    product = splitNumArray(product)
    count++
  }
  return num < 10 ? 0 : count
}