js省市级联菜单

<meta http-equiv=”Content-Type” content=”text/html; charset=UTF-8″ />
<!DOCTYPE HTML PUBLIC “-//W3C//DTD HTML 4.0 Transitional//EN”>
<html>
<head>
<title>New Document </title>
<script language=”JavaScript”>

var city=
[
 ["北京","天津","上海","重庆"],
 ["南京","苏州","南通","常州"],
 ["福州","福安","龙岩","南平"],
 ["广州","潮阳","潮州","澄海"],
 ["兰州","白银","定西","敦煌"]
 ];
function getCity(){  //定义getCity()函数
 var sltProvince=document.getElementById(“province”);
 //定义sltProvince变量, document.getElementByid(“province”)取得<select id=province的值>
 var sltCity=document.getElementById(“city”);
 //取得<select id=city的值>
 var provinceCity=city[sltProvince.selectedIndex-1];//定义数组长度，由于数组下标从0开始，所以减1
 //city[sltprovince.selectedIndex-1],这里的selectedIndex就不明白了，拜托讲得详细一些
 
 sltCity.length=1;//这里也不太明白，length是什么,为什么赋值1
 //length是select的option数组长度，初始值为1，因为默认有只有一个选项‘请选择所在城市’
 for(var i=0;i<provinceCity.length;i++){     //
 sltCity[i+1]=new Option(provinceCity[i],provinceCity[i]);//
 }
}

 </script>
 </head>
 <body>

 <form>
 <select name=”province” id=”province” onchange=”getCity()”>
  <option value=”0″>请选择所在省份</option>
  <option value=”直辖市”>直辖市</option>
  <option value=”江苏省”>江苏省</option>
  <option value=”福建省”>福建省</option>
  <option value=”广东省”>广东省</option>
  <option value=”甘肃省”>甘肃省</option>
 </select>
 <select id=”city” name=”city”>
  <option value=”0″>请选择所在城市</option>
 </select>
</form>
 </body>
 </html>