Projects:Client Side Event Handlers Extension PreDelete/QA
An example can be found in Openbravo source code 
The developed example:
- On change functions to ensure backwards compatibility.
- Pre-Delete actions
- Client side validation
- Server side validation, by calling an Action Handler.
A test case can be found in testLink under: 3.0 Test Suite > Platform > Client Side Event Handlers Test
It has been verified that this development has no performance implications in the application while executing this actions.