Javascript Backbone.js为什么可以'；不要使用父get方法

奇怪的是，我将这两部分代码放在两个文件中，base.js和filter.js： //泛型对象类的定义

var baseObject = Backbone.Model.extend({
    copy: function(){
        _clipBoard=this;
    },
    fetch: function(){
        var obj =this;
        var criteriaString = encodeURI(JSON.stringify({_id:this.get("_id")}));
        var getUrl = _rootUrl+'/nalab/'+this.getMongoType()+'/';
        $.getJSON(getUrl + "_find", 'criteria=' + criteriaString, function(data){
            var results = data.results;
            obj.set(results[0]);
        });
    }
});

//definition of a baseObject subclass called filter with speical methods
var Filter = baseObject.extend({
    getTitleField : function(){
        return 'title';
    },
    getMongoType: function(){
        return 'filter';
    }
});

然后我在firefox 5中执行以下代码：

var filter = new Filter({_id:{$oid:"4e43ca017c36ec707b755659"}});
filter.fetch();
console.log(filter);
/*
Firebug shows an object with "attributes" that contains a field 'title'='Filtres avances'
*/
console.log(filter.get('title');
/*
Firebug says undefined
*/

---

那个么，为什么“super”get方法对Filter类不起作用，尽管它对baseObject类起作用并且从不重写它呢？

因为您试图在ajax请求完成并且数据设置为model之前获取

title

。 如果要获取数据，请尝试以下操作：

var filter = new Filter({_id:{$oid:"4e43ca017c36ec707b755659"}});
filter.bind('change', function(model) {
    console.log(model.get('title');
});
filter.fetch();