Converted draft code to Coffeescript, and added calculation for number of weeks in the year

example.html

@@ -59,6 +59,49 @@
       });
     });
   </script>
+  <h3>Formatting Dates With Weeks</h3>
+  <div id="graph-weeks" class="graph"></div>
+  <script>
+    $(function () {
+      // data stolen from http://howmanyleft.co.uk/vehicle/jaguar_'e'_type
+      var week_data = [
+        {"period": "2011 W27", "licensed": 3407, "sorned": 660},
+        {"period": "2011 W26", "licensed": 3351, "sorned": 629},
+        {"period": "2011 W25", "licensed": 3269, "sorned": 618},
+        {"period": "2011 W24", "licensed": 3246, "sorned": 661},
+        {"period": "2011 W23", "licensed": 3257, "sorned": 667},
+        {"period": "2011 W22", "licensed": 3248, "sorned": 627},
+        {"period": "2011 W21", "licensed": 3171, "sorned": 660},
+        {"period": "2011 W20", "licensed": 3171, "sorned": 676},
+        {"period": "2011 W19", "licensed": 3201, "sorned": 656},
+        {"period": "2011 W18", "licensed": 3215, "sorned": 622},
+        {"period": "2011 W17", "licensed": 3148, "sorned": 632},
+        {"period": "2011 W16", "licensed": 3155, "sorned": 681},
+        {"period": "2011 W15", "licensed": 3190, "sorned": 667},
+        {"period": "2011 W14", "licensed": 3226, "sorned": 620},
+        {"period": "2011 W13", "licensed": 3245, "sorned": 0},
+        {"period": "2011 W12", "licensed": 3289, "sorned": 0},
+        {"period": "2011 W11", "licensed": 3263, "sorned": 0},
+        {"period": "2011 W10", "licensed": 3189, "sorned": 0},
+        {"period": "2011 W09", "licensed": 3079, "sorned": 0},
+        {"period": "2011 W08", "licensed": 3085, "sorned": 0},
+        {"period": "2011 W07", "licensed": 3055, "sorned": 0},
+        {"period": "2011 W06", "licensed": 3063, "sorned": 0},
+        {"period": "2011 W05", "licensed": 2943, "sorned": 0},
+        {"period": "2011 W04", "licensed": 2806, "sorned": 0},
+        {"period": "2011 W03", "licensed": 2674, "sorned": 0},
+        {"period": "2011 W02", "licensed": 1702, "sorned": 0},
+        {"period": "2011 W01", "licensed": 1732, "sorned": 0}
+      ];
+      Morris.Line({
+        element: 'graph-weeks',
+        data: week_data,
+        xkey: 'period',
+        ykeys: ['licensed', 'sorned'],
+        labels: ['Licensed', 'SORN']
+      });
+    });
+  </script>  
      
   <h3>Formatting Dates with YYYY-MM</h3>
   <div id="graph-yyyy-mm" class="graph"></div>

morris.coffee

@@ -288,8 +288,20 @@ class Morris.Line
     m = s.match /^(\d+) Q(\d)$/
     n = s.match /^(\d+)-(\d+)$/
     o = s.match /^(\d+)-(\d+)-(\d+)$/
+    p = s.match /^(\d+) W(\d+)$/
     if m
       parseInt(m[1], 10) + (parseInt(m[2], 10) * 3 - 1) / 12
+    else if p
+      # calculate number of weeks in year given
+      year = parseInt(p[1], 10);
+      y1 = new Date(year, 0, 1);
+      y2 = new Date(year+1, 0, 1);
+      if y1.getDay() isnt 4
+        y1.setMonth(0, 1 + ((4 - y1.getDay()) + 7) % 7);
+      if y2.getDay() isnt 4
+        y2.setMonth(0, 1 + ((4 - y2.getDay()) + 7) % 7);
+      weeks = 1 + Math.ceil((y2 - y1) / 604800000);
+      parseInt(p[1], 10) + (parseInt(p[2], 10) - 1) / weeks;
     else if n
       parseInt(n[1], 10) + (parseInt(n[2], 10) - 1) / 12
     else if o

morris.js

@@ -314,16 +314,22 @@
     };
 
     Line.prototype.parseYear = function(date) {
-      var day, m, month, n, o, s, timestamp, y1, y2, year;
+      var day, m, month, n, o, p, s, timestamp, weeks, y1, y2, year;
       s = date.toString();
       m = s.match(/^(\d+) Q(\d)$/);
       n = s.match(/^(\d+)-(\d+)$/);
       o = s.match(/^(\d+)-(\d+)-(\d+)$/);
-      p = s.match(/^(\d+) W(\d)$/);
+      p = s.match(/^(\d+) W(\d+)$/);
       if (m) {
         return parseInt(m[1], 10) + (parseInt(m[2], 10) * 3 - 1) / 12;
       } else if (p) {
-        return parseInt(p[1], 10) + (parseInt(p[2], 10) - 1) / 53;
+        year = parseInt(p[1], 10);
+        y1 = new Date(year, 0, 1);
+        y2 = new Date(year + 1, 0, 1);
+        if (y1.getDay() !== 4) y1.setMonth(0, 1 + ((4 - y1.getDay()) + 7) % 7);
+        if (y2.getDay() !== 4) y2.setMonth(0, 1 + ((4 - y2.getDay()) + 7) % 7);
+        weeks = 1 + Math.ceil((y2 - y1) / 604800000);
+        return parseInt(p[1], 10) + (parseInt(p[2], 10) - 1) / weeks;
       } else if (n) {
         return parseInt(n[1], 10) + (parseInt(n[2], 10) - 1) / 12;
       } else if (o) {