EasyUI-combotree 的使用&&选择叶子节点控制

<input class="easyui-combotree" id="systemTree" style="width:200px;">

$('#systemTree').combotree({
        url: '${ctx}/rcSystem/list?pid=1',
        valueField: 'id',
        textField: 'text',
        required: false,
        editable: false,
        animate:true,
        onBeforeExpand:function(node,param){
            $('#systemTree').combotree("tree").tree("options").url = "${ctx}/rcSystem/list?pid=" + node.id;
        },
        onBeforeSelect : function(node) {
            //只能选择叶子节点
            if (!$(this).tree('isLeaf', node.target)) {  
                return false;  
            }
        },
        onSelect : function(node) {
            
        },
        onLoadSuccess: function (node, data) {
            
        }
       });