Javascript to add days to date field

I have five radio buttons that I am trying to add days to the current date field on the form to new field--due date.

First four are relatively easier. But the last 'type5' is part of the radio group that I was wondering if I can include federal holidays to be accounted for in the date calculation. If that is not possible or too complex, is it possible to have that selection be freeform text (user can enter date based off the date format)?

var date = new Date();

var addTime = this.getField("group1").value;

var days = 0;
if (addTime != "Off") {
    switch (addTime) {
    case "type1" :
        days = 10;
        break;
    case "type2" :
        days = 5;
        break;
    case "type3" :
        days = 60;
        break;
    case "type4" :
        days = 10;
        break;   
    }
    date.setDate(date.getDate()+days);
    event.value = util.printd("mm/dd/yyyy", date);
}
else {
    event.value = "";
}