Learning Oldvalue - It returns an empty value

[PurviP]

Problem Statement: 
When oldValue is used in onChange client scripts, it always returns an empty value.

An example:

onChange client script depends on the Short description field. When the client script triggered, the oldValue is returning empty instead of what the user previously entered in the Short description field prior to saving the change.

Client Script:

g_form.addInfoMessage('<b> old value: </b>' + oldValue + ' ||  <b> New value: </b>' + newValue);