code: function (funcName, $window) {
          var vendors = ['webkit', 'moz'],
              func;
          for (var i = 0; i < vendors.length && !func; ++i) {
              var vp = vendors[i];
              func = $window[vp + funcName];
          }
          return func;
      }
docs: adapted from https://github.com/darius/requestAnimationFrame/blob/master/requestAnimationFrame.js