D3 Examples - modest map problem

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<!DOCTYPE html>
<html>
<head>
<title>Modest Maps JS</title>
<script type="text/javascript" src="https://cdn.jsdelivr.net/gh/stamen/modestmaps-js/modestmaps.js"></script>
<script type="text/javascript">
    var map;
    function initMap() {
        
        // some test
        function Test() { }
        Test.prototype.getTile = function(coord) {
            var div = document.createElement('div');
            div.innerHTML = 'test';
            return div;
        }
        MM.extend(Test, MM.MapProvider);
​
​
        fg = new MM.Layer(new Test());
        map = new MM.Map(document.body, [fg]);
        
        map.setCenterZoom(new MM.Location(0, 0), 2);
    }
</script>
<style>
html, body {
  width: 100%; height: 100%;
}
</style>
</head>
<body onload="initMap()">
</body>
</html>
    