RadBtn is a static object that allows easy reading and manipulation of radio button and checkbox properties.
This demonstration focuses on radio buttons, however checkboxes are treated identically.

This form is called 'f1' and the button set is called 'r1'.

Tom  Dick  Harry  Pete

Action Required Function Call for Button Set Above
RadBtn.enableAll(document.forms.f1.r1, false);
RadBtn.enableAll(document.forms.f1.r1, true);
RadBtn.select(document.forms.f1.r1, 3);
v = RadBtn.getValue(document.forms.f1.r1);
v = RadBtn.getIndex(document.forms.f1.r1);

If the form cannot have a name attribute, give it an ID and use: document.getElementById('formId').r1

Access Instructions and Source Code