Iterate list with JavaScript

Hello everyone!

I'm working on a nintex form based on a list. Is it possible, to Iterate on this list with the form Custom JavaScript option? My main problem is, that i don't know how to call the list. It would be important, to iterate and SumIf one of the columns, before insert a new element. Thinking about something like this:

NWF.FormFiller.Events.RegisterAfterReady(function(){
NWF$('#' + JDrop).change(function(){
var Sum = 0;

for (var i = 0; i < MyList.count; i++)

{
 if (MyList[i,2].value == NWF$('#' + JDrop).val())
  { Sum=Sum+MyList[i,3].value; }
  }
NWF$('#' + MyJavaValue).val(Sum);
});});

Where i have no clue, what to use at the place of "MyList"

Thanks for any idea.