如何在回调函数后访问和打印 JSON 对象值

Question

如何在 .on 方法完成循环我的 firebase 中的所有项目并递增所有值后打印“obj”值？简而言之，我在这里要做的是，一旦循环完成，我想将结果（“obj”）打印到控制台。

在这里感谢任何帮助！谢谢。

var obj = {
    "20120101" : {"neutral": 0, "positive": 1, "negative": 2},
    "20120101" : {"neutral": 0, "positive": 1, "negative": 2}
} //above is just an example on the structure of the object

var fbase = new Firebase("https://<appname>.firebaseio.com/");
fbase.on('child_added', function(snapshot){
    var item = snapshot.val(); //has the attributes of: date & classification
    var date_str = item.date;
    if (!obj[date_str]){
        //initialise the counting;
        obj[date_str] = { "negative": 0, "neutral": 0, "positive" : 0 };
    }
    obj[date_str][item.classification] += 1;
});
console.log(obj);

Answer 1

在查阅了 Firebase 文档后，我终于找到了我的问题的答案： https://www.firebase.com/docs/javascript/datasnapshot/index.html

这是我更新的代码，以防有人遇到同样的问题：

var obj = {
    "20120101" : {"neutral": 0, "positive": 1, "negative": 2},
    "20120101" : {"neutral": 0, "positive": 1, "negative": 2}
} //above is just an example on the structure of the object

var fbase = new Firebase("https://<appname>.firebaseio.com/");
fbase.once('value', function(allMessagesSnapshot) {
    allMessagesSnapshot.forEach(function(messageSnapshot) {
        var date = messageSnapshot.child('date').val();
        var classification = messageSnapshot.child('classification').val();
        // Do something with message.
        if (!obj[date]){
            obj[date] = { "negative": 0, "neutral": 0, "positive" : 0 };
        }
        obj[date][classification] += 1;
    });
    console.log(obj);
});

感谢您的回答，不胜感激！ :D

Answer 2

你必须把它放在回调中：

var obj = {
    "20120101" : {"neutral": 0, "positive": 1, "negative": 2},
    "20120101" : {"neutral": 0, "positive": 1, "negative": 2}
} //above is just an example on the structure of the object

var fbase = new Firebase("https://<appname>.firebaseio.com/");
fbase.on('child_added', function(snapshot){
    var item = snapshot.val(); //has the attributes of: date & classification
    var date_str = item.date;
    if (!obj[date_str]){
        //initialise the counting;
        obj[date_str] = { "negative": 0, "neutral": 0, "positive" : 0 };
    }
    obj[date_str][item.classification] += 1;
    console.log(obj);
});

因为回调会在以后的某个时间调用，因此数据可用的唯一位置是回调内部或您可能从回调调用的任何函数中。