title: in zebra datepicker how can i get or extract week number from selected date?
body: <p>below is my attempt, but it doesn't work.  the first line is to initialize the datepicker, then there are some options that can be set, then in the onSelect section is how i was trying to get the selected and convert to a week number, then for testing i was just trying to alert the week number.  once i get it to work i will put the week number somewhere for use.</p>
  
  <pre><code>$("input#someid").Zebra_DatePicker({
  format: 'm-d-Y',
  direction: 1,
  show_clear_date: 'FALSE',
  onSelect: function(view, elements) { //when a date is selected
      Date.prototype.getWeek = function() {
          var onejan = new Date(this.getFullYear(),0,1);
          return Math.ceil((((this - onejan) / 86400000) + onejan.getDay()+1)/7);
      }
      var myvariable = $( "#someid" ).val();
      var weekno = myvariable.getWeek();
      alert(weekno);
  }
  });
  </code></pre>
  
  <p>the format of the date matters.  it needs to be able to convert from m-d-Y (01-13-2014) format to a week number.  so for example, today's date would have a result of 3 because it's the 3rd week of the year.</p>