datagrid 动态生成列

$('#dd').datagrid({
singleSelect: true,
columns: [[]]
});

loaddata(row.ASITEMCODE);

function loaddata(asItemCode) {
var url = "../server/aaa.jsp"
$.ajax({
type: "post",
url: url,
success: function(msg) {
$("#dd").datagrid({
columns: new Array(eval(eval('(' + msg + ')').COLUMNS))
}).datagrid("loadData", eval('(' + msg + ')'));
}
});
}

String columns = "[{field:\"OPNO\",title:\"考核登记编号\",width:65},{field:\"TRANSTIME\",title:\"当前系统时间\",width:65}]";