Javascript 在Meteor中，observeChanges中的this.added和this.change未按预期运行

我很抱歉标题含糊不清，帖子很长，但我很难描述我的行为。我试着用任何一种方式来解释

我有一个新闻提要页面，在那里我可以显示帖子。我只想显示比用户打开页面时旧的帖子，这样列表就保持被动，而不会在顶部添加新帖子。因此，我决定在发布函数中使用observeChanges，如下所示：

Newsfeed = new Mongo.Collection('newsfeed');

if (Meteor.isServer) {
    Meteor.publish("newsfeed", function (init_last_activity, limit) {
        var self = this;

        check(limit, Number);
        check(init_last_activity, Date);

        var init = true,
            count = 0;

        var handle = Newsfeed.find({},{
            'limit': limit,
            'sort': {'updated_time': -1}
        }).observeChanges({
            // when a post is added, we check if it's got an older
            // updated_time than the initial updated time field
            // generated on init and only if so, we display
            // the post to the client
            added: function(id, doc) {
                count++;
                console.log('++++ POST NR. ' + count + ' ++++ ('+id+')');
                console.log('Updated time:  ', doc.updated_time);
                console.log('Last activity: ', init_last_activity);

                if (doc.updated_time < init_last_activity) {
                    console.log('- - - - -');
                    console.log('ADDED!');

                    self.added('newsfeed', id, doc);

                    console.log('ID: ' + id);
                    console.log(' ');
                }
            },

            changed: function(id, fields) {
                console.log('Trigger changed for id:', id);
                self.changed('newsfeed', id, fields);
            }
        });

        init = false;

        this.ready();

        this.onStop(function() {
            handle.stop();
        });
    });
}

如您所见，有两篇文章被发送到客户端。现在，当同一个用户在几秒钟后试图“喜欢”第二个post ID:7pt3nbkkqgckj4g5fc时，会触发上述代码中的self.change，这种情况会发生：

I20141024-20:21:13.997(-7)? Trigger changed for id: 7pt3nBKqgCKJ4G5fc
I20141024-20:21:13.997(-7)? Exception in queued task: Error: Could not find element with id 7pt3nBKqgCKJ4G5fc to change
I20141024-20:21:13.997(-7)?     at _.extend.changed (packages/ddp/livedata_server.js:185)
I20141024-20:21:13.997(-7)?     at _.extend.changed (packages/ddp/livedata_server.js:397)
I20141024-20:21:13.997(-7)?     at _.extend.changed (packages/ddp/livedata_server.js:1154)
I20141024-20:21:13.997(-7)?     at Newsfeed.find.observeChanges.changed (app/collections/newsfeed.js:125:22)
I20141024-20:21:13.998(-7)?     at packages/mongo/observe_multiplex.js:163
I20141024-20:21:13.998(-7)?     at Array.forEach (native)
I20141024-20:21:13.998(-7)?     at Function._.each._.forEach (packages/underscore/underscore.js:105)
I20141024-20:21:13.998(-7)?     at Object.task (packages/mongo/observe_multiplex.js:157)
I20141024-20:21:13.998(-7)?     at _.extend._run (packages/meteor/fiber_helpers.js:145)
I20141024-20:21:13.998(-7)?     at packages/meteor/fiber_helpers.js:123

与几秒钟前附加到self.added函数的id完全相同。奇怪的是，如果我跳过if语句，不管发生什么都允许self.added运行，那么一切都会正常工作：

added: function(id, doc) {
    self.added('newsfeed', id, doc);
}

因此，尽管在前面的示例中调用了self.added，但似乎仅仅因为在if语句中调用self.added就破坏了代码

---

有人知道为什么会这样吗？我是否误解了添加和更改的功能？我很困惑：

这是一篇老文章，但我想我在这个链接上找到了一个错误的线索：所以对于将来遇到这个问题的人，请查看GitHub上的链接。

added: function(id, doc) {
    self.added('newsfeed', id, doc);
}