function largestNumberIndex(numArray) {
  const largestNumberInfos = numArray.reduce(
    function(acc, val, index) {
      if (val > acc[1]) {
        return [index, val];
      }
      return acc;
    },
    [0, numArray[0],]
  );
  return largestNumberInfos[0];
}

function orderArray(numArray) {
  const finalResult = numArray.reduce(
    function(acc) {
      const finalArray = acc[0];
      const currentArrayToOrder = acc[1];
      const largestIndex = largestNumberIndex(currentArrayToOrder);
      const numArrayCopy = currentArrayToOrder.slice();
      const removedNumber = numArrayCopy.splice(largestIndex, 1)[0];
      finalArray.push(removedNumber);

      return [finalArray, numArrayCopy];
    },
    [[], numArray]
  );
  return finalResult[0];
}

console.log(orderArray([5, 10, 7, 8]));