function sum(numberOne) {
      var count = numberOne;
      return function by(numberTwo) {
        if (numberTwo === undefined) {
          return count;
        } else {
          count += numberTwo;
          return by;
        }                            
      }
}
console.log(sum(10)(12)(30)());

function sum(x) {
    var result = 0;
    for(var i=0;i<arguments.length;i++){
        result += arguments[i];
    }
    var foo = function(){
        for(var i=0;i<arguments.length;i++){
            result += arguments[i];
        }
        return foo;
    };
    foo.toString = function(){
        return result;
    };
    return foo;
}

console.log(+sum(10)(12)(30));

function sum (n) {     
    var v = function (x) {
        return sum (n + x);
    };
    v.valueOf = v.toString = function () {
        return n;
    };
    return v;
}

console.log(+sum(10)(12)(30));