Change functions based on jQuery plugin {options}
In my opinion it's a good idea to get rid of the switch case by using better naming for the inputs and by changing the structure of your functions to Object based functions, i.e. if you change your functions to this:

var showDate={
    all:function (){
        alert(d.toString());
    },
    date:function showDateOnly(){
        alert(d.toDateString());
    },
    time:function (){
        alert(d.toLocaleTimeString());
    }
};


and the setting options you get are ['all' , 'date' , 'time']

then you can call these functions like this:

(showDate[settings.date]) ? showDate[settings.date]() : showDate.all();


and get rid of the switch case. DEMO