Google Maps Clusterer

How to get this thing work?

My code is:

<script type="text/javascript" src="http://maps.google.com/maps/api/js?sensor=false"></script> 
<script type="text/javas开发者_开发知识库cript">
    var markers = [];
    var markerClusterer = null;
    var map = null;

    function initialize()
    {
        var center = new google.maps.LatLng(65, 45);
        var options = {
            'zoom': 4,
            'center': center,
            'mapTypeId': google.maps.MapTypeId.ROADMAP
        };

        map = new google.maps.Map(document.getElementById("map"), options);
        markerClusterer = new MarkerClusterer(map);
        alert(1);
    }
    $(document).ready(function() { initialize(); });
</script>

I can't even get alert(1);?

What I did wrong?