EasyUI选项卡避免重复打开

前台代码：

<div data-options="region:'west',title:'我的工作平台',split:true,iconCls:'icon-desk'"  style="width: 200px;">
        <div id="aa" class="easyui-accordion" style="width: 300px; height: 200px;" data-options="fit:true">
            <div title="xx" data-options="iconCls:'icon-save',selected:true" style="overflow: auto; padding: 10px;">
                <ul id="tab1" class="easyui-tree">                  
                    <li id="Purchase.html">
                        <span>xxxx</span>
                    </li>
                     <li id="">
                        <span>xxxx</span>
                    </li>
                     <li id="">
                        <span>xxxx</span>
                    </li>
                </ul>
            </div>
            <div title="xx" data-options="iconCls:'icon-inStorage'" style="padding: 10px;">
                <ul id="Ul1" class="easyui-tree">
                    <li id="Li2">
                        <span>xxxx</span>
                    </li>
                    <li id="Li3">
                        <span>xxxx</span>
                    </li>
                    <li id="Li4">
                        <span>xxxx</span>
                    </li>
                </ul>
            </div>                              
        </div>
    </div>
    <div data-options="region:'center'" style="padding: 5px; background: #eee;">
       <div id="tabs" class="easyui-tabs" data-options="fit:true">
            <div title="主控台" id="mainimg"></div>
        </div>
    </div>

js代码：

$(function () {
    $(".easyui-tree").tree({
        onClick: function (node) {
            AddTab(node.text, node.id);
        }
    });

    function AddTab(title, url) {

       //判断选项卡是否重复打开
        if ($('#tabs').tabs('exists', title)) {
            $('#tabs').tabs('select', title);//选中并刷新
        } else {
            var content = createFrame(url); //创建Frame
            $("#tabs").tabs("add", {
                title: title,
                content: content,
                closable: true

            })
        }
       
    }
    //创建Frame
    function createFrame(url) {
        var tabHeight = $("#tabs").height() - 35;
        var s = '<iframe scrolling="auto" frameborder="0"  src="' + url + '" style="width:100%;height:' + tabHeight + 'px;"></iframe>';
        return s;
    }

});