easy ui datagrid 设置冻结列

$('#tt').datagrid({
title:'Frozen Columns',
iconCls:'icon-save',
width:500,
height:250,
url:'data/datagrid_data.json',
frozenColumns:[[
{field:'itemid',title:'Item ID',width:80},
{field:'productid',title:'Product ID',width:80},
]],
columns:[[
{field:'listprice',title:'List Price',width:80,align:'right'},
{field:'unitcost',title:'Unit Cost',width:80,align:'right'},
{field:'attr1',title:'Attribute',width:100},
{field:'status',title:'Status',width:60}
]]
});

<table id="tt" title="Frozen Columns" class="easyui-datagrid" style="width:500px;height:250px"
url="data/datagrid_data.json"
singleSelect="true" iconCls="icon-save">
<thead frozen="true">
<tr>
<th field="itemid" width="80">Item ID</th>
<th field="productid" width="80">Product ID</th>
</tr>
</thead>
<thead>
<tr>
<th field="listprice" width="80" align="right">List Price</th>
<th field="unitcost" width="80" align="right">Unit Cost</th>
<th field="attr1" width="150">Attribute</th>
<th field="status" width="60" align="center">Stauts</th>
</tr>
</thead>
</table>