用meteor开发网页时html中的seletc 默认选项的设置

select的默认选中项总是不对，还以为是meteor的关系，用时差不多一天终于找到问题所在：

<label for="app-type" class="col-sm-2 control-label">应用分类*:</label><div class="col-sm-3">    <select class="form-control" id="app-type">        <option value="">请选择应用分类</option>        {{#each appcategorys}}            <option value="{{_id}}" selected="{{apptypeSelected _id}}">{{name}}</option>        {{/each}}    </select></div>
Template.editapp.helpers({    appcategorys:function(){        console.log("appcategorys this.categoryid:"+this.categoryid+ " this.subcategoryid:"+this.subcategoryid);        oldcategoryid=this.categoryid;        oldsubcategoryid=this.subcategoryid;        oldprocesstype=this.processtype;        return categoryRecords.find({state:1});    },    apptypeSelected:function(categoryid){        console.log('apptypeSelected categoryid:'+categoryid+ " oldcategoryid:"+oldcategoryid);        if(categoryid===oldcategoryid){            console.log('apptypeSelected categoryid===oldcategoryid');            return 'selected';        }        return '';//正确是应该返回undefined;    }});原来问题就出在这里，apptypeSelected中return 时不能返回 ‘’,应该返回undefined;