Cannot read property '__e3_' of undefined
<p>Have seen a few of these errors dotted around here, but having looked at the answers, I haven't yet found a solution that works here. All seems to work fine until I add in the eventListener for 'click' to open up an infoWindow, which is when I receive the following error in console:</p>

<p><em>Cannot read property '__e3_' of undefined</em></p>

<p>Any ideas as to what is causing this error? </p>

<p>Note that I am far from an expert in using Google Maps, so please bear that in mind with any answers :)</p>

<pre><code>&lt;div class="acf-map c-location-map" style="width: 100%; height: 700px;"&gt;
    &lt;?php 

        // Get a list of all offices, we need their IDs to get their locations for use with the Google map.
        $stockistList = get_posts(array(
            'posts_per_page'    =&gt; -1,
            'post_type'         =&gt; 'stockist',
        ));

        if (!empty($stockistList))          
        {
            foreach ($stockistList as $singleStockist)
            {
                // Create a simple div that shows the map working correctly.
                printf('&lt;div class="c-location-map__marker marker" data-country="%s"&gt;
                            &lt;h4&gt;%s&lt;/h4&gt;
                        &lt;/div&gt;', 
                        get_field('stockist_country', $singleStockist-&gt;ID),
                        $singleStockist-&gt;post_title
                    );
            }
        }
    ?&gt;
&lt;!-- .c-location-map --&gt;&lt;/div&gt;

&lt;script type="text/javascript"&gt;
(function($) {

/**
 * Creates a new Google Map using the markers on the page. 
 */
function ts_newMap($el) 
{   
    var $markers = $el.find('.marker');

    // Settings
    var args = {
        zoom                : 3,
        center              : new google.maps.LatLng(0, 0),
        mapTypeId           : google.maps.MapTypeId.ROADMAP,
        scrollwheel         : false,
        styles              : [{"featureType":"all","elementType":"all","stylers":[{"visibility":"simplified"}]},{"featureType":"all","elementType":"geometry","stylers":[{"color":"#0025f0"}]},{"featureType":"all","elementType":"geometry.fill","stylers":[{"visibility":"simplified"},{"color":"#2d3a6d"}]},{"featureType":"all","elementType":"labels","stylers":[{"visibility":"off"}]},{"featureType":"all","elementType":"labels.text.fill","stylers":[{"gamma":0.01},{"lightness":20}]},{"featureType":"all","elementType":"labels.text.stroke","stylers":[{"saturation":-31},{"lightness":-33},{"weight":2},{"gamma":0.8}]},{"featureType":"all","elementType":"labels.icon","stylers":[{"visibility":"off"}]},{"featureType":"administrative.country","elementType":"labels","stylers":[{"visibility":"off"}]},{"featureType":"administrative.province","elementType":"labels","stylers":[{"visibility":"off"}]},{"featureType":"administrative.locality","elementType":"labels","stylers":[{"visibility":"off"}]},{"featureType":"administrative.neighborhood","elementType":"labels","stylers":[{"visibility":"off"}]},{"featureType":"administrative.land_parcel","elementType":"labels","stylers":[{"visibility":"off"}]},{"featureType":"landscape","elementType":"geometry","stylers":[{"lightness":30},{"saturation":30},{"visibility":"simplified"},{"color":"#636363"}]},{"featureType":"landscape","elementType":"labels","stylers":[{"visibility":"off"}]},{"featureType":"poi","elementType":"all","stylers":[{"color":"#636363"}]},{"featureType":"poi","elementType":"geometry","stylers":[{"saturation":20}]},{"featureType":"poi","elementType":"labels","stylers":[{"visibility":"off"}]},{"featureType":"poi.park","elementType":"geometry","stylers":[{"lightness":20},{"saturation":-20}]},{"featureType":"road","elementType":"all","stylers":[{"visibility":"simplified"},{"color":"#636363"}]},{"featureType":"road","elementType":"geometry","stylers":[{"lightness":10},{"saturation":-30}]},{"featureType":"road","elementType":"geometry.stroke","stylers":[{"saturation":25},{"lightness":25}]},{"featureType":"road","elementType":"labels","stylers":[{"visibility":"off"}]},{"featureType":"transit","elementType":"all","stylers":[{"visibility":"simplified"},{"color":"#636363"}]},{"featureType":"transit","elementType":"labels","stylers":[{"visibility":"off"}]},{"featureType":"water","elementType":"all","stylers":[{"lightness":-20},{"visibility":"simplified"},{"color":"#efefed"}]},{"featureType":"water","elementType":"labels","stylers":[{"visibility":"off"}]}]
    };

    // create map               
    var map = new google.maps.Map( $el[0], args);

    // add a markers reference
    map.markers = [];   

    // add markers
    $markers.each(function() {  
        ts_newMapMarker($(this), map);      
    });

    // Centre the map based on what pins have been added.
    ts_mapCentre(map);

    // return
    return map;
}

/**
 * Adds an individual marker to the map.
 */
function ts_newMapMarker($marker, map)
{

    var marker;

    var dataCountry = $marker.attr('data-country');
    console.log("Country: " + dataCountry);

    geocoder = new google.maps.Geocoder();
    function getCountry(country) {
        geocoder.geocode( { 'address': country }, function(results, status) {
            if (status == google.maps.GeocoderStatus.OK) {
                map.setCenter(results[0].geometry.location);
                marker = new google.maps.Marker({
                    map: map,
                    position: results[0].geometry.location,
                    icon    : '&lt;?php bloginfo('template_url'); ?&gt;/assets/images/map-marker.png'
                });
            } else {
                alert("Geocode was not successful for the following reason: " + status);
            }
        });
    }

    map.markers.push( marker );

    getCountry(dataCountry);

    // if marker contains HTML, add it to an infoWindow
    if($marker.html())
    {
        // create info window
        var infowindow = new google.maps.InfoWindow({
            content     : $marker.html()
        });

        // show info window when marker is clicked
        google.maps.event.addListener(marker, 'click', function() {
            console.log("open info window");
            infowindow.open( map, marker );
        });
    }

}

/**
 *  Centres the map based on what's been added to it.
 */
function ts_mapCentre(map)
{
    // vars
    var bounds = new google.maps.LatLngBounds();

    // loop through all markers and create bounds
    $.each( map.markers, function(i, marker)
    {
        var latlng = new google.maps.LatLng(marker.position.lat(), marker.position.lng());
        bounds.extend( latlng );
    });

    // only 1 marker?
    if( map.markers.length == 1 )
    {
        // set center of map
        map.setCenter(bounds.getCenter());
        map.setZoom(8);
    }
    else {
        // fit to bounds
        map.fitBounds(bounds);
    }

}

/**
 *  Build the map now the page is ready.
 */
var map = null;
$(document).ready(function()
{
    $('.acf-map').each(function()
    {
        // create map
        map = ts_newMap($(this));
    });
});

})(jQuery);
&lt;/script&gt;
</code></pre>