Google Maps API: markerwithlabel.js - Uncaught Ref

I have read the docs and examples, but I it seems I cannot solve the initialization error ("Uncaught ReferenceError: google is not defined" + Uncaught ReferenceError: homeLatLng is not defined) when trying to include markerwithlabel.js file and it's reminds me to the "you cannot load something before the map is done" prob.

What can I do?

What was tried:

<head>
<script async defer src="https://maps.googleapis.com/maps/api/js?key=mykey&callback=initMap"></script>
<script type="text/javascript" src="http://google-maps-utility-library-v3.googlecode.com/svn/trunk/markerwithlabel/src/markerwithlabel.js"></script>
<script type="text/javascript"> 
    var map;
    function initMap() {

            map = new google.maps.Map(document.getElementById('map'), {
                zoom: 14,
                center: {lat: 52.5200066, lng: 13.404954}
            });

            var marker1 = new MarkerWithLabel({
                   position: homeLatLng,
                   draggable: true,
                   raiseOnDrag: true,
                   map: map,
                   labelContent: "$425K",
                   labelAnchor: new google.maps.Point(22, 0),
                   labelClass: "labels", // the CSS class for the label
                   labelStyle: {opacity: 0.75}
            });
    }
</script>

markerwithlabel.js requires a already loaded maps-API.

When you load the maps-API asynchronously(as you do in your code), there is no guarantee that the maps-API is loaded when markerwithlabel.js will be loaded.

solution: load the maps-API synchronously

<script src="https://maps.googleapis.com/maps/api/js?v=3&key=mykey"></script>
<script type="text/javascript" src="http://google-maps-utility-library-v3.googlecode.com/svn/trunk/markerwithlabel/src/markerwithlabel.js"></script>
<script type="text/javascript"> 
    var map;
    function initMap() {

            map = new google.maps.Map(document.getElementById('map'), {
                zoom: 14,
                center: {lat: 52.5200066, lng: 13.404954}
            });

            var marker1 = new MarkerWithLabel({
                   position: homeLatLng,
                   draggable: true,
                   raiseOnDrag: true,
                   map: map,
                   labelContent: "$425K",
                   labelAnchor: new google.maps.Point(22, 0),
                   labelClass: "labels", // the CSS class for the label
                   labelStyle: {opacity: 0.75}
            });
    }
google.maps.event.addDomListener(window, 'load', initMap);
</script>