backbone.js - 下划线“后”功能

Question

我有类似的代码

(function(exports, $, Backbone, document){
    "use strict";

    var modals = {
        "Alerts.alert_delete" : (function() {
            var self = this;    
            return {
                template : {
                    count : this.collection.length,
                    models : this.collection.models
                },
                events : {
                    "click .confirm" : function(event) {
                        event.preventDefault();
                        var modal = this,
                            finished = _.after(modal.collection.length, self.reDraw);

                        // Models are succesfully delete, but finished is not completed 
                        this.collection.each(function(model) {
                            modal.collection.sync('delete', model, { success : finished });
                        });
                    }
                }
            };
        })
    };

    exports.app.modal = function(name, context) {
        return modals[name].call(context);
    };
}(this, jQuery, Backbone, document));

请忽略抽象，这是为了允许我对所有模态使用一个通用视图，同时保持独特的逻辑抽象。我不知道为什么_.after函数在被正确调用次数后没有完成。self在这种情况下是对父视图的引用。

有人可以为我解释一下吗？