js/leaflet.markercluster.js
function (cluster) {
    var childCount = cluster.getChildCount();

    var c = ' marker-cluster-';
    if (childCount < 10) {
      c += 'small';
    } else if (childCount < 100) {
      c += 'medium';
    } else {
      c += 'large';
    }

    return new L.DivIcon({ html: '<div><span>' + childCount + '</span></div>', className: 'marker-cluster' + c, iconSize: new L.Point(40, 40) });
  }
function (cluster) {
    var childCount = cluster.getChildCount();

    var c = ' marker-cluster-';
    if (childCount < 10) {
      c += 'small';
    } else if (childCount < 100) {
      c += 'medium';
    } else {
      c += 'large';
    }

    return new L.DivIcon({ html: '<div><span>' + childCount + '</span></div>', className: 'marker-cluster' + c, iconSize: new L.Point(40, 40) });
  }
Default functionality