JS 获取JSON格式数据对象值

<span style="white-space:pre">		</span>var json;
//var str = {"code":0,"data":[{"uid":"689791","username":"vaghyuzhihao","orgid":"627","status":"1","subname":"yuzhihao","roleids":"1","orgcode":"600251","name":"yuzhihao","mapid":"0","passwd":"","siteid":"0","createorgcode":"600251","alarmview":"0"}]};
//var str = {"code":0,"data":[{"uid":"689791","alarmview":"0"}]};
var str = {"code":0, "addResults": [ { "objectId": "120555935", "success": "true" } ] };
if(typeof str === 'object'){
json = str;
}
else{
json = eval(str);// 如果打印不成功 此处改为  eval("("+str+")");
}
alert(json.addResults[0].objectId);