javawscript 三级菜单的实现原理

==请选择乡镇==威海文登荣成乳山

省份,城市，区县数据结构：【名称，父类ID,当前ID】

 onChange="changelocation2(document.editForm.smalllocation.options[document.editForm.smalllocation.selectedIndex].value)"

根据selectedIndex取得下一级关联菜单的父类ID,
复制代码 代码如下:
function changelocation(locationid)
{
document.editForm.smalllocation.length = 0;
// document.editForm.dlmc0.length = 0;
document.getElementById("dlmc0").length=0;
//document.editForm.dlmc0.options[0] = new Option('==请选择==','');
document.getElementById("dlmc0").options[0] = new Option('==请选择==','');

//alert(locationid);
var locationid=locationid;
var i;
document.editForm.smalllocation.options[0] = new Option('==请选择==','');
for (i=0;i < onecount; i++)
{
if (subcat[i][1] == locationid)
{
document.editForm.smalllocation.options[document.editForm.smalllocation.length] = new Option(subcat[i][0], subcat[i][2]);
}
}
}