code: function() {
          var exist = false;
          if(this.clusters && this.clusters.length > 0 &&
             this.clusters.length == this.layer.features.length) {
              exist = true;
              for(var i=0; i<this.clusters.length; ++i) {
                  if(this.clusters[i] != this.layer.features[i]) {
                      exist = false;
                      break;
                  }
              }
          }
          return exist;
      }
docs: Method: clustersExist
  Determine whether calculated clusters are already on the layer.
  
  Returns:
  {Boolean} The calculated clusters are already on the layer.