未捕获的TypeError：对象[object Object]没有方法'selectedBases'

Question

任何想法我做错了什么？因为我收到错误消息未捕获TypeError：对象[object Object]没有方法'selectedBases'下面是我的代码

this.selectedBases = ko.observable();
        this.selectedBases.subscribe(function (options) {
             if(options.length >0){
                if (options.find('select_all')) {
                    self.selectedBases(options.intersect('select_all'));
                } 
            } 
        });