JS 获取JSON格式数据对象值

应用场景：与ArcGIS Server 服务通讯，添加feature对象后，返回JSON格式数据，获取添加成功后的OBJECTID.

		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);