Catalog Item Client Script for Dependent Drop Down Box

Hi,

I am trying to create a Client Script for a Catalog Item where a Select Box choices are dependent on selection of other Select box options. What is the simplest way of achieving this? I was thinking of using OnChange client script.

The Select Box fields are:

1. Request Type

2. Access Extension

3. Contract Extension

Request type:
Onboard
Offboard

Access Extension

Extension Type: (if Request Type = Access Extension)
Contract Extension
Employee Extension

Contract Extension: (if Extension Type = Contract Extension)
Labour Hire
Contractor for Service
Consultant
Technology Service Partners

Contract Extension (if Extension Type = Employee Extension)
Non-ongoing