// requires raf.js (polyfil)

(function(){
   var ids = {};

   function requestId(){
      var id;
      while (!id || ids.hasOwnProperty(id)){
        id = Math.floor(Math.random() * 1E9);
      };
      return id;
   }

   if (!window.requestNextAnimationFrame) {
      window.requestNextAnimationFrame = function(callback, element) {
         var id = requestId();

         ids[id] = requestAnimationFrame(function(){
            ids[id] = requestAnimationFrame(function(ts){
               delete ids[id];
               callback(ts);
            },element);
         },element);

         return id;
      };
   }

   if (!window.cancelNextAnimationFrame) {
      window.cancelNextAnimationFrame = function(id) {
         if (ids[id]) {
            cancelAnimationFrame(ids[id]);
            delete ids[id];
         }
      };
   }
})();