In JavaScript, there is no point to implement pure observer pattern as in Java, because JavaScript has this little thing called functional programming. So just use something like http://api.jquery.com/category/callbacks-object/ instead of your ObserverList.

If you still want to use your object, then everything depends on what do you want to pass to ObserverList.Add. If it is some object, then you need to write

for( i = 0; i < observers.Count; i++) { observers[i].Notify("some data"); }

If it is a function then you need to write

for( i = 0; i < observers.Count; i++) { observers[i]("Some data"); }