Given a number, this method returns an ordered array of its factors.

getFactors.js

const getFactors = num => {
  const maxFactorNum = Math.floor(Math.sqrt(num));
  const factorArr = [];
  let count = 0; // count of factors found < maxFactorNum

  for (let i = 1; i <= maxFactorNum; i++) {
    //inserting new elements in the middle using splice
    if (num % i === 0) {
      //(index, how many to remove, inserted element)
      factorArr.splice(count, 0, i);
      const otherFactor = num / i;
      if (i !== otherFactor) {
        //insert these factors in the front of the array
        factorArr.splice(-count, 0, otherFactor);
      }
      count++;
    }
  }

  //swapping first and last elements
  const lastIndex = factorArr.length - 1;
  const temp = factorArr[lastIndex];
  factorArr[lastIndex] = factorArr[0];
  factorArr[0] = temp;

  return factorArr;
};