二级下拉框

<script language="javascript">
        var cities=[
            ["运营管理部","商务客服"],
            ["供应链部","售后部","物流管理部","采购经理","IT工程师"],
            ["总部财务部","财务经理"],
            ["苹果分销事业部","产品经理"],
            ["苹果零售事业部","产品经理"],
            ["华为零售事业部","产品经理","商务"],
            ["新零售事业部","产品经理"],
            ["安徽分公司","分公司总经理","人事行政","分公司财务经理","分公司会计","苹果零售经理","MONO专员","华为零售经理","华为零售拓展经理","华为零售市场经理","华为零售培训经理","苹果分销经理","苹果市场经理","分销业务经理","三星产品经理","魅族产品经理","综合市场经理","代销仓管理主任","办事处经理","客户代表"],
            ["南京仓","分仓经理","分仓主管","客服","售后","运输/调度","仓管员"],
            ["杭州仓","分仓经理","分仓主管","客服","售后","运输/调度","仓管员"],
            ["上海仓","分仓经理","分仓主管","客服","售后","运输/调度","仓管员"],

            
         
        ];
        function show(val){
            for(i=0;i<cities.length;i++){ //循环遍历，一维数组长度
                if(cities[i][0]==val){  //一维数组下标为0的元素即省 与下拉菜单值比较
                    document.getElementById("city").length=1;  // city 长度设为1
                    for(j=1;j<cities[i].length;j++){ //循环遍历，二维数组长度
                        document.getElementById("city").add(
                        new Option(cities[i][j]));  //给city赋新cities选出的值

                    }
                }

            }
        }
    </script>