check arguments and closure in a function in javascript

–JS File

function solution(para) {
  if(arguments.length == 0){
    return 'Please pass a argument';
  } else if(arguments.length > 1){
    var finalN = 0;
    for(var i=0; i<arguments.length; i++){
      finalN += arguments[i];
    }
    return finalN;
  } else {
    return function(para2){
      return para + para2;
    }
  }
}

Only closure

function Solution(n) {
   var myFun = function(x) {
      return add(n + (x === undefined ? 0 : x));
   };
   myFun.valueOf = function () {
      return n;
   };
   return myFun;
}