Perfect number checker

perfect-number.js

/**
 * Indicates whether the sum of the factors of a number
 * are equal to the number
 * https://en.wikipedia.org/wiki/Perfect_number
 * 
 * @param {Number} num
 * @returns {Boolean}
 */
function isPerfectNumber (num) {
  const numRoot = Math.sqrt(num)
  const isEven = num % 2 === 0
  const incr = isEven ? 1 : 2
  let factorsSum = 1

  for (let factor = isEven ? 2 : 3; factor <= numRoot; factor += incr) {
    if (num % factor === 0) {
      const compliment = num / factor

      factorsSum += factor
      if (compliment !== factor) {
        factorsSum += compliment
      }
    }
  }

  return factorsSum === num
}