JavaScript 实现N级联动的下拉列表

<form name="form1" method="post">
<select id="s1" name="s1"></select><select id="s2" name="s2"></select><select id="s3" name="s3"></select><select id="s4" name="s4"></select>
</form>
<script language="JavaScript">
<!--
function LianDong(arr, sel)
{
var me = this;
this.$ = function(o)
{
return document.getElementById(o);
}

this.sub = function (i, pid)
{
for (var j=i+1; j<sel.length; j++)
{
me.$(sel[j]).length = 0;
me.$(sel[j]).options[0] = new Option("请选择", "");
}
for ( var j = 0; j < arr.length; j++)
{
if (arr[j][1] == pid)
{
me.$(sel[i+1]).options[me.$(sel[i+1]).length] = new Option(arr[j][2], arr[j][0]);
}
}
}

this.init = function()
{
me.sub(-1,"root");
for (var i=0; i<sel.length-1; i++)
{
me.$(sel[i]).onchange = function()
{
var i;
for (i=0; me.$(sel[i])!=this; i++);
me.sub(i, me.$(sel[i]).value);
}
}
}

this.init();
}

var array=new Array();
array[0]=new Array("华南地区","root","华南地区");
array[1]=new Array("华北地区","root","华北地区");
array[2]=new Array("上海","华南地区","上海");
array[3]=new Array("广东","华南地区","广东");
array[4]=new Array("徐家汇","上海","徐家汇");
array[5]=new Array("普托","上海","普托");
array[6]=new Array("广州","广东","广州");
array[7]=new Array("湛江","广东","湛江");
array[8]=new Array("湛江1","湛江","湛江1");
array[9]=new Array("湛江2","湛江","湛江2");
array[10]=new Array("广州1","广州","广州1");
array[11]=new Array("广州2","广州","广州2");

var select = new Array("s1","s2","s3","s4");

var liandong=new LianDong(array, select)
//-->
</script>