js 问题，新手求教

代码如下，当我把显示热力图语句{ heatmapOverlay = new BMapLib.HeatmapOverlay({"radius": 104}); map.addOverlay(heatmapOverlay); heatmapOverlay.setDataSet({data: p4, max: 100}); heatmapOverlay.show(); } 写到函数 show_heat_map();里后调用该函数不显示热力图，但是当我把上面的司机话写入<script> </script>里面（也就是不用函数）时可以显示热力图，请问这是怎么回事？求指教！

{% block page_content %} {% block scripts %} {{ super() }} <script type="text/javascript" src="{{" url_for('static',="" filename="js/jquery.js" )="" }}=""></script> <script type="text/javascript" src="<a href=" http:="" <a="" href="http://api.map.baidu.com" rel="nofollow">api.map.baidu.com="" api?v="2.0&ak="" rel="nofollow">http://api.map.baidu.com/api?v=2.0&ak="></script> {# 热力图 js 文件#} <script type="text/javascript" src="{{" url_for('static',="" filename="js/Heatmap_min.js" )="" }}=""></script>

{% endblock %}

<div id="allmap" style="width: 100%; height: 600px; float: left"></div>

<script>
    var map = new BMap.Map("allmap"); // 关闭底图可点动能
    map.enableScrollWheelZoom();       // 鼠标滚动缩放
    var point = new BMap.Point(117.051534, 36.660632);
    map.centerAndZoom(point, 16);

    var points = [];
    var p4 = [{"lng": 117.035278, "lat": 36.666162, "count": 99}];
    


    $.getJSON($SCRIPT_ROOT + '/jquery/all_loads_nodes', {}, function (data) {
        var nodes = data.result['nodes'];
        var loads = data.result['loads'];
        loads.forEach(function (load) {
            var start_id = load[0];
            var end_id = load[1];
            var start_lng = Number(nodes[start_id]['longitude']);
            var start_lat = Number(nodes[start_id]['latitude']);
            var end_lng = Number(nodes[end_id]['longitude']);
            var end_lat = Number(nodes[end_id]['latitude']);
            var k = (start_lat - end_lat) / (start_lng - end_lng);
            var step = (start_lng - end_lng) / 10;
            var flow = load[4];

            for (var i = 0; i <= 2; i++) {
                var point = {
                    "lng": Number((end_lng + i * step).toFixed(6)),
                    "lat": Number((k * i * step + end_lat).toFixed(6)),
                    "count": parseInt(flow / 150)
                };
                points.push(point);
            }
        });
        show_heat_map();
    });

    function show_heat_map() {
    	heatmapOverlay = new BMapLib.HeatmapOverlay({"radius": 104});
    	map.addOverlay(heatmapOverlay);
        heatmapOverlay.setDataSet({data: p4, max: 100});
        heatmapOverlay.show();

    }

</script>