From a script include perspective, I'm lost on how to do that (or it's just not coming to me at the moment.) This is the script include I have.

var DateValidator = Class.create();
DateValidator.prototype = Object.extendsObject(AbstractAjaxProcessor, {

    validateDate: function() {
        var selectedDateStr = this.getParameter('selectedDate'); // Get date from the client
        var selectedDate = new GlideDateTime(); // Convert to GlideDateTime 

		var output = this._checkHoliday(selectedDateStr, "8-5 weekdays excluding holidays");
		//gs.info("DateValidator: " + selectedDateStr + " Holiday is: " + output );
		return output;
    },
    _checkHoliday: function(myDateTime, scheduleName) {
		var blockedDay = false; // initalize holiday to false
        var schedule = new GlideRecord('cmn_schedule');
        schedule.addQuery('name', '8-5 weekdays excluding holidays');
        schedule.query();
        if (schedule.next()) {
            var sched = new GlideSchedule(schedule.sys_id);
            var d = new GlideDateTime();
            d.setDisplayValue(myDateTime); // setting myDateTime 
            if (sched.isInSchedule(d))
                blockedDay = false; // not a holiday or weekend
            else
                blockedDay = true; // holiday or weekend
        }
		
		return blockedDay;

    },
});