Small script that listens for categories selected on the OpenSesame course upload page. It then uses the selected options to reveal radio button options that the user will be required to choose from in order to select a primary category for their course.

showPrimary.js

var subjects = jQuery('#edit-field-course-subjects-taxonomy-und');
function displayPrimarySubject(){
  var subjectVal =[];
	var subjectInput = subjects.find('input:checked');
	subjectInput.each(function(){ 
	var catVal= jQuery(this).val();
	subjectVal.push(catVal);
	});
	var primarySubjectField= jQuery('#edit-field-primary-subject');
	if (subjectVal.length > 0){
	primarySubjectField.show();
		var primarySubjects = jQuery('#edit-field-primary-subject-und').find('input');
		primarySubjects.each(function(){
			var selectedSubject = jQuery(this);
			var optionVal = jQuery(this).val(); 
			var returnVal = jQuery.inArray(optionVal, subjectVal);
			
			if(returnVal > -1){
			console.log(returnVal);
			selectedSubject.parent().show();
			}else{
			selectedSubject.parent().hide();
			}

			});
		
	} else{
		primarySubjectField.hide();
	}
}
displayPrimarySubject();
subjects.find('input').click(function(){
	displayPrimarySubject();
});