Security:Strawman Model

$ cat Iterator.js function Iterator() {

   var i = arguments.length;

   if (i < 0 && 2 < i)
       throw TypeError("Iterator requires 0 to 2 arguments");

   function generic_next() { return this(); };

   var arg0 = arguments[0];
   if (arg0 && typeof arg0 == "object") {
       if (i == 2 && typeof arg0 == "function") {
           var callable = arg0;
           var sentinel = arguments[1];
           var last;

           function funiter() {
               last = callable();
               if (last == sentinel)
                   throw "StopIteration";
               return last;
           }
           funiter.next = generic_next;
           funiter.done = function () { return last == sentinel; };
           return funiter;
       }

       var keys = [];
       for (i in arg0)
           keys.push(i);

       i = 0;
       function objiter() {
           if (i == keys.length)
               throw "StopIteration";
           return keys[i++];
       }
       objiter.next = generic_next;
       objiter.done = function () { return i == keys.length; };
       return objiter;
   }

   var end, start = 0, step = 1;
   i = 0;
   switch (arguments.length) {
     case 3:
       step = Number(arguments[2]);
     case 2:
       start = Number(arg0), i = 1;
     case 1:
       end = Number(arguments[i]);
       break;
   }

   i = start;
   function iter() {
       if (i == end)
           throw "StopIteration";
       var j = i;
       i += step;
       return j;
   }
   iter.next = generic_next;
   iter.done = function () { return i == end; };
   return iter;

}