select option 的自定义属性 传值 问题？

    js部分代码如下：

mui.plusReady(function(){  
            var add_detail_fla = document.getElementById("add_detail_fla");  
            var add_nowdetail_fla = document.getElementById("add_nowdetail_fla");//区划显示  

            mui.getJSON('assets/address.json',null,function(data){  
                    var area_html = "";  
                    plus.nativeUI.toast("开始获取辖区信息");  
                    area_html += '<option value="" selected="selected">请选择所在区</option>';  
                    for (i=0;i<data.length;i++) {  
                        area_html += '<option value="'+data[i].v+'" grade="'+JSON.stringify(data[i].s)+'" >'+data[i].t+'</option>';  
                        console.log("data[i].s -- "+JSON.stringify(data[i].s));  
                    }  
                    document.getElementById('add_area_fla').innerHTML = area_html;  
            });  

        });  

        function setStreet(){  
            var street = document.getElementById('add_area_fla');  
            var data = street.options[street.selectedIndex].getAttribute("grade");  
            console.log("setStreet -- "+data.length+" -- "+data.s+" -- "+data);  
            console.log();  
                var street_html = "";  
                street_html += '<option value="" selected="selected">请选择所在街道</option>';  
                for(i=0;i<data.length;i++){  
                    street_html += '<option value="'+data[i].v+'" grade="'+data[i].s+'" >'+data[i].t+'</option>';  
                }  
                document.getElementById("add_street_fla").innerHTML = street_html;  
        }  

        function setCommity(){  
            var comity = document.getElementById('add_commity_fla');  
            var data = comity.options[comity.selectedIndex].getAttribute("grade");  
            console.log("setCommity data -- "+data);  
        }  

HTML代码如下：

<form class="mui-input-group mainCont">  
                <ul class="mui-table-view">  
                    <li>  
                        <div class="icon"><img src="../img/icon3.jpg"></div>  
                        <select name="add_area_fla" id="add_area_fla" onchange="setStreet()" >  
                        </select>  
                    </li>  
                    <li>  
                        <div class="icon"><img src="../img/icon3.jpg"></div>  
                        <select name="add_street_fla" id="add_street_fla" onchange="setCommity()" >  
                        </select>  
                    </li>  
                    <li>  
                        <div class="icon"><img src="../img/icon3.jpg"></div>  
                        <select name="add_commity_fla" id="add_commity_fla"  >  
                        </select>  
                    </li>  
                </ul>  
        </form>