js/leaflet.markercluster.js
function () {
    if (!this.options.removeOutsideVisibleBounds) {
      return this.getBounds();
    }

    var map = this._map,
      bounds = map.getBounds(),
      sw = bounds._southWest,
      ne = bounds._northEast,
      latDiff = L.Browser.mobile ? 0 : Math.abs(sw.lat - ne.lat),
      lngDiff = L.Browser.mobile ? 0 : Math.abs(sw.lng - ne.lng);

    return new L.LatLngBounds(
      new L.LatLng(sw.lat - latDiff, sw.lng - lngDiff, true),
      new L.LatLng(ne.lat + latDiff, ne.lng + lngDiff, true));
  }
function () {
    if (!this.options.removeOutsideVisibleBounds) {
      return this.getBounds();
    }

    var map = this._map,
      bounds = map.getBounds(),
      sw = bounds._southWest,
      ne = bounds._northEast,
      latDiff = L.Browser.mobile ? 0 : Math.abs(sw.lat - ne.lat),
      lngDiff = L.Browser.mobile ? 0 : Math.abs(sw.lng - ne.lng);

    return new L.LatLngBounds(
      new L.LatLng(sw.lat - latDiff, sw.lng - lngDiff, true),
      new L.LatLng(ne.lat + latDiff, ne.lng + lngDiff, true));
  }
function ( ) { if ( ! this . options . removeOutsideVisibleBounds ) { return this . getBounds ( ) ; } var map = this . _map , bounds = map . getBounds ( ) , sw = bounds . _southWest , ne = bounds . _northEast , latDiff = L . Browser . mobile ? 0 : Math . abs ( sw . lat - ne . lat ) , lngDiff = L . Browser . mobile ? 0 : Math . abs ( sw . lng - ne . lng ) ; return new L . LatLngBounds ( new L . LatLng ( sw . lat - latDiff , sw . lng - lngDiff , true ) , new L . LatLng ( ne . lat + latDiff , ne . lng + lngDiff , true ) ) ; }
Gets the maps visible bounds expanded in each direction by the size of the screen (so the user cannot see an area we do not cover in one pan)
Gets the maps visible bounds expanded in each direction by the size of the screen ( so the user cannot see an area we do not cover in one pan )