marker_cluster.js

var L = window.L;
var addressPoints = window.addressPoints;
var tiles = L.tileLayer('http://{s}.tile.osm.org/{z}/{x}/{y}.png', {
    maxZoom: 18,
    attribution: '&copy; <a href="http://osm.org/copyright">OpenStreetMap</a> contributors, Points &copy 2012 LINZ'
  }),
  latlng = L.latLng(-37.82, 175.24);

var map = L.map('map', {
  center: latlng,
  zoom: 13,
  layers: [tiles]
});

console.log(L.DivIcon.prototype);

var markers = L.markerClusterGroup({
  
  iconCreateFunction: function createMarker(cluster) {
    var markers = cluster.getAllChildMarkers();
    var title = '';
    for (var i = 0; i < markers.length; i++) {
      title += markers[i].options.data[2] + ',';
    }
    return new L.DivIcon({
      html: '<div class="marker">' + title + '</div>'
    });
  }
  
});

var CustomMarker = L.Marker.extend({
  options: {
    data: {}
  }
});

function loop(i) {
  var a = addressPoints[i];
  var title = a[2];
  var marker = new CustomMarker(new L.LatLng(a[0], a[1]), {
    title: title,
    data: a
  });
  marker.bindPopup(title);
  markers.addLayer(marker);
  if (addressPoints[i]) {
    setTimeout(function() {
      loop(i + 1);
    }, 300);
  }
}

loop(0);


map.addLayer(markers);