acrobat javascript when checkbox is checked, make separate field required

Being a designer, not a coder, I have limited coding ability. I have created an acrobat form with a number of due date fields. They are only required if a corresponding checkbox is checked.

What is the javascript to say that 'if checkbox A is checked, then make date field A required'?

Also, do I save this as a document javascript, or link it to the checkbox? Thanks