实现效果
选择相应的省份，二级菜单默认显示省会城市，同时可以选择其他城市。
源码
<!DOCTYPE html><html lang="en"><head><meta charset="UTF-8"><title>Title</title><script>/*** 实现二级菜单级联*/var provinces=[{id:1001,name:'江苏省',cities:[{id:1,name:'南京市'},{id:2,name:'苏州市'},{id:3,name:'扬州市'},{id:4,name:'徐州市'},{id:5,name:'常州市'}]},{id:1002,name:'山东省',cities:[{id:1,name:'济南市'},{id:2,name:'青岛市'},{id:3,name:'威海市'},{id:4,name:'烟台市'},{id:5,name:'德州市'}]},{id:1003,name:'广东省',cities:[{id:1,name:'广州市'},{id:2,name:'东莞市'},{id:3,name:'青远市'},{id:4,name:'佛山市'},{id:5,name:'深圳市'}]}];window.onload = function(){var province = document.getElementById("province");var city = document.getElementById("city");province.onchange = function(){// 清除之前city下拉框内的数据,只留下第一个optionif(city.length>1){city.length = 1;}var selected = provinces[province.selectedIndex-1]; //被选中省份的JSON对象for(var i=0;i<selected.cities.length;i++){//城市的name作为文本，城市的id作为value,创建新的option对象var option = new Option(selected.cities[i].name,selected.cities[i].id); city.add(option);//将option对象添加到city的末尾}city.selectedIndex = 1; //默认显示第二个option，即省会城市 }}</script></head><body>省份：<select id = "province"><option value="0">--请选择省份--</option><option value="1">江苏省</option><option value="2">山东省</option><option value="3">广东省</option></select>城市：<select id="city"><option value="0">--请选择城市--</option></select></body></html>
