2个下拉框，选择1级菜单后，2级菜单出现相应的备选项。如果没有选择则不能提交。
先创建html文件
<!DOCTYPE html> <html> <head> <title></title> </head> <body> <form> <select> <option selected="selected">请选择...</option> </select> <select> <option selected="selected">请选择...</option> </select> <button type="submit" disabled="disabled">提交</button> </form> </body> <script type="text/javascript"> var provinces=['辽宁','北京','上海','吉林','浙江']; //最新添加的省份放在最前面 var choice=['请选择...'] var zhejiang=['杭州','嘉兴','宁波','绍兴']; var shanghai=['金山','闸北','普陀','徐汇']; var jilin=['长春','辽源','吉林','四平']; var beijing=['海淀','朝阳','东城','西城']; var liaoning=['沈阳','大连','盘锦','锦州','辽阳','鞍山'] //城市排序由后到前 var citys=new Array; citys[0]=choice; citys[1]=zhejiang; citys[2]=jilin; citys[3]=shanghai; citys[4]=beijing; citys[5]=liaoning; function add_option(select,option){ var target=document.getElementById(select); for (var i = option.length - 1; i >= 0; i--) { var add_option=document.createElement("option"); add_option.text=option[i]; target.add(add_option,null); target.lastChild.setAttribute("name",option[i]); } } add_option("province",provinces); document.getElementById("province").addEventListener("change",function(){ var selevted_province=document.getElementById("province"); var selected_city=document.getElementById("city"); for (var i = selevted_province.length - 1; i >= 0; i--) { selected_city.remove(i); } var selected=selevted_province.selectedIndex; if (selected==0) { add_option("city",citys[0]); document.getElementById("where_submit").setAttribute("disabled","ture"); }else{ add_option("city",citys[selected]); document.getElementById("where_submit").removeAttribute("disabled"); } }) </script> </html>