Get Weeks in a Month in Jquery DateTimePicker Week

Question

Current I am using Jquery DatePicker as my Calender picker in one of my project. My Requirement is to get the week number also added in each month's Calender display. Also for every month, week should start from 1 to 4 or 5. How I can write a function "fnweek" and pass this function in calculateWeek parameter?

$('#date').datesPicker({          
    firstDay : 1,
    showWeek:true,
    calculateWeek: fnweek
});

function fnweek(){
}

Thanks for the help.