extjs ajax 返回值如何写

function classSchool(value){
var result;
Ext.Ajax.request({
url:'test.aspx?cmd=getclsh',
params:{classID:value},
success:function(response,result){
var data = Ext.decode(response.responseText);
result = data.value;
alert(result+'____');
},
failure:function(){
Ext.Msg.alert('提示','数据库连接错误！');
return 0;
}
});
return result;
}
alert(classSchool('11111'));

后台：
if (cmd == "getclsh")
{
string classID = Request["classID"].ToString().Trim();

res = "{value:'22222'}";

Response.Write(res);
Response.End();
}