map
Map the values in this list to another list.
    list.map(callback[, thisArg])
  
  Loops through the values of the list, calling callback for each one until the list
ends.  The return values of callback are used to populate the returned list.
var todos = new DefineList([
  {name: "dishes", complete: false},
  {name: "lawn", complete: true}
]);
var names = todos.map(function(todo){
  return todo.name;
});
names //-> DefineList["dishes","lawn"]
  
  Parameters
- callback 
{function(item, index, list)}:A function to call with each element of the DefineList. The three parameters that callback gets passed are:
- item (*) - the element at index.
 - index (Integer) - the index of the current element of the list.
 - list (DefineList) - the 
DefineListthe elements are coming from. 
The return value of
callback, includingundefinedvalues are used to populate the resulting list. - thisArg 
{Object}:The object to use as
thisinside the callback.