Calculate ISO 8601 Week Number from SharePoint Date Picker

Hi All,

I am looking to Calculate the ISO 8601 Week Number (1-52) from a SharePoint Date Picker, and output the Week Number to another SharePoint field (Single line of text).

Date Picker Field: DateOfWork

Text Field: ISOWeek

So far i have got:

var WorkDate = $("input[title='DateOfWork']").val
$('WorkDate').datepicker({ 
     onSelect: function(dateText, inst) {
        alert($.datepicker.iso8601Week(new Date(dateText)))
     } 
});

and i want to Insert the ISO 8601 Week into a the ISOWeek like so:

 $("input[title='ISOWeek']").val(WorkDate);

Any ideas?

Thanks, Tucker