Function overloading

index.js

function average() {
  // the number of arguments passed
  const length = arguments.length;

  if (length == 0) return 0;

  // convert the arguments to a proper array of numbers
  const numbers = Array.prototype.slice.call(arguments);

  // a reducer function to sum up array items
  const sumReduceFn = function (a, b) { return a + Number(b) };

  // return the sum of array items divided by the number of items
  return numbers.reduce(sumReduceFn, 0) / length;
}