[JavaScript] СÁ·Ï° Arguments Optional

function addTogether() {
  var args = Array.from(arguments);
  return args.some(arg => typeof(arg)!=='number')?
    undefined:
    args.length > 1 ?
      args.reduce((acc,n) => acc+=n, 0):
      (n) => typeof n === "number" ? 
        n+args[0]:
        undefined;
}

addTogether(2,3);