省市二级菜单php实现（一）

<select name="sf" onChange="document.all.modifys1s2s3.src = 's2.php?s2=' + this.value +'&s3='+ document.all.ss.value">
<option selected>省份</option>
</select>
&nbsp;
<select name="ss" onChange="document.all.modifys1s2s3.src = 's2.php?s2='+document.all.sf.value +'&s3='+ this.value">
  <option selected>地级市</option>
</select>
&nbsp;
<select name="sx">
<option selected>市、县级市、县</option> 
</select>
<script language='JAVASCRIPT' id='modifys1s2s3'>
var k2=document.all.sf.value;
var k3=document.all.ss.value;
if(k2>0 && k3=='undefined')
{
document.all.modifys1s2s3.src = 's2.php?s2='+document.all.sf.value + '&s3=0';
}
else
{
document.all.modifys1s2s3.src = 's2.php?s2='+document.all.sf.value + '&s3='+document.all.ss.value;
}
</script>

同样的实现比asp节约很多的资源。。转（二）