js/leaflet.markercluster.js
function (map) {
    map.off('zoomend', this._zoomEnd, this);
    map.off('moveend', this._moveEnd, this);

    this._unbindEvents();

    //In case we are in a cluster animation
    this._map._mapPane.className = this._map._mapPane.className.replace(' leaflet-cluster-anim', '');

    if (this._spiderfierOnRemove) { //TODO FIXME: Not sure how to have spiderfier add something on here nicely
      this._spiderfierOnRemove();
    }



    //Clean up all the layers we added to the map
    this._hideCoverage();
    this._featureGroup.onRemove(map);
    this._nonPointGroup.onRemove(map);

    this._featureGroup.clearLayers();

    this._map = null;
  }
function (map) {
    map.off('zoomend', this._zoomEnd, this);
    map.off('moveend', this._moveEnd, this);

    this._unbindEvents();

    //In case we are in a cluster animation
    this._map._mapPane.className = this._map._mapPane.className.replace(' leaflet-cluster-anim', '');

    if (this._spiderfierOnRemove) { //TODO FIXME: Not sure how to have spiderfier add something on here nicely
      this._spiderfierOnRemove();
    }



    //Clean up all the layers we added to the map
    this._hideCoverage();
    this._featureGroup.onRemove(map);
    this._nonPointGroup.onRemove(map);

    this._featureGroup.clearLayers();

    this._map = null;
  }
Overrides FeatureGroup.onRemove