marker_popup.js

/* jshint devel:true */
L.mapbox.accessToken = '*************************';
var id = 1;
var map = L.mapbox.map('map', 'mapbox.dc-markers');

var markers = [];
var currentIndex;

// Open popup when user mouses over a marker
map.featureLayer.on('ready', function(e) {
    this.eachLayer(function(marker) {
        var marker.id = id;
        var index = markers.length - 1;
    	markers.push(marker); 
    	console.log(marker._leaflet_id);
    	id++;
    });

	var content = '<button class="next-marker" onclick="nextMarker('+ (index + 1) +')">Next</button>';
	this.bindPopup(content);
});

map.on('popupopen', function(e) {
  var marker = e.popup._source;
  currentIndex = findIndex(markers, 'id', marker.id);
  console.log(marker);
  document.getElementById('next-marker').onclick = nextMarker;
});

function nextMarker(index){
  markers[index].closePopup();
  markers[index + 1].openPopup();
}

function previousMarker(index){
  markers[index].closePopup();
  markers[index - 1].openPopup();
}

function findIndex(array, key, value){
  var index = -1;
  array.forEach(function(item, i){
    if(item[key] === value){
      index = i;
    }
  });
  return index;
}