ObservableList class created in this recipe will use the features of the framework's
Ext.util.Observable class to fire notifications when items are added, removed, or when the list is cleared. The list's interface will be as follows:
add(object):A function that inserts an item in the list and returns the position into which the item was inserted
insert(index, object):A function that inserts an item to the
Listat the specified index
item(index):A function that returns the element at the specified index
remove(object):A function to remove the first occurrence of a specific object ...