Disable the Apply changes button until changes have been made

[rjollos]

Disable the Apply changes button until one of the following events has occurred:

• One of the default radio buttons has been selected.
• The list has unsaved changes.

[rjollos]

(In [12437]) Refs #10694: Apply changes button is disabled until a change has been made.

[rjollos]

In [12437] I have 3 instances of $('#enumtable div input[name="apply"]'). Do you think it is worth extract this into a variable? I don't see any performance issues here, but I've read recommendations that repeated execution of a selector should be avoided when possibly for performance reasons. I'm primarily concerned that this could reduce code clarity. I could equally see it as improving code clarity though.

Another recommendation I've read, but have yet to see in any jquery code, is that variables that contain selectors should be named starting with $. For example, $apply = $('#enumtable div input[name="apply"]'). Is that variable naming pattern commonly used?