forEach
Call a function for each element of a DefineList.
    list.forEach(callback[, thisArg])
  
  Loops through the values of the list, calling callback for each one until the list ends
or false is returned.
list.forEach(function(item, index, list){ ... })
  
  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 - the current element of the list.
 - list - the DefineList the elements are coming from.
 
If the callback returns
falsethe looping stops. - thisArg 
{Object}:The object to use as
thisinside the callback. 
Use
forEach calls a callback for each element in the DefineList.
var list = new DefineList([1, 2, 3]);
list.forEach(function(element, index, list) {
    list.get(index, element * element);
});
list.get(); // [1, 4, 9]