后台返回的json取值

  function down_kcd(tsk_id,index,a_obj){
      $.post(
     "hblims/sample/taskSampleList!queryTaskKcd.action",
     {tsk_id:tsk_id},
     function(data){
     alert(data);
       var obj = eval("(" + data + ")");//转换后的JSON对象
       var att_id = obj.EXP_SOLUTION_ATT_ID;
       alert('attId ='+att_id);
       if(att_id!=null){
        a_obj.href='<%=basePath%>/hblims/task/taskAction!downLoadFile.action?&attId='+att_id;
       // eval(a_obj.href());
       }else{
           a_obj.href="JavaScript:$.messager.alert('提示','此任务写不存在勘察方案!')";
       }
     }
    );
  }