解除dom循環引用導致的內存泄露

function purge(d) {
   var a = d.attributes, i, l, n;
   if (a) {
      l = a.length;
      for (i = 0; i < l; i += 1) {
         n = a[i].name;
         if (typeof d[n] === 'function') {
         d[n] = null;
         }
      }
   }
   a = d.childnodes;
   if (a) {
      l = a.length;
         for (i = 0; i < l; i += 1) {
            purge(d.childnodes[i]);
         }
   }
}