<!-- 要实现此效果需要 1 个步骤： -->
<!-- 第 1 步： -->
<!-- 把下面的代码加到<BODY></BODY>区域中： -->
<script language="JavaScript">
<!--
var subcat = new Array();
subcat[0] = new Array('10','1','=1')
subcat[1] = new Array('10','2','=2')
subcat[2] = new Array('10','3','=3')
subcat[3] = new Array('10','4','=4')
subcat[4] = new Array('10','5','=5')
subcat[5] = new Array('10','6','=6')
subcat[6] = new Array('10','7','=7')
subcat[7] = new Array('10','8','=8')
subcat[8] = new Array('10','9','=9')
subcat[9] = new Array('10','10','=10')
subcat[10] = new Array('20','11','=11')
subcat[11] = new Array('20','12','=12')
subcat[12] = new Array('20','13','=13')
subcat[13] = new Array('20','14','=14')
subcat[14] = new Array('20','15','=15')
subcat[15] = new Array('20','16','=16')
subcat[16] = new Array('20','17','=17')
subcat[17] = new Array('20','18','=18')
subcat[18] = new Array('20','19','=19')
subcat[19] = new Array('20','20','=20')
function changeselect1(locationid)
{
document.form1.s2.length = 0; //清空s2的值
document.form1.s2.options[0] = new Option('==请选择==','');
for (i=0; i<subcat.length; i++)
{
if (subcat[i][0] == locationid)
{document.form1.s2.options[document.form1.s2.length] = new Option(subcat[i][1], subcat[i][2]);}
//document.form1.s2.length—— s2.option的数目，首次循环为0.
}
}
//-->
</script>
<form name="form1">
二级联动：
<select name="s1" onChange="changeselect1(this.value)">
<option>==请选择==</option>
<option value="10">1-10</option>
<option value="20">11-20</option>
</select>
<select name="s2" onChange="alert(this.value)">
<option>==请选择==</option>
</select>
</form>
<!-- 二级联动 Over -->
<!-- 三级联动 Start -->
<script language="JavaScript">
<!--
var subval = new Array();
subval[0] = new Array('10','单数','1','=1')
subval[1] = new Array('10','双数','2','=2')
subval[2] = new Array('10','单数','3','=3')
subval[3] = new Array('10','双数','4','=4')
subval[4] = new Array('10','单数','5','=5')
subval[5] = new Array('10','双数','6','=6')
subval[6] = new Array('10','单数','7','=7')
subval[7] = new Array('10','双数','8','=8')
subval[8] = new Array('10','单数','9','=9')
subval[9] = new Array('10','双数','10','=10')
subval[10] = new Array('20','单数','11','=11')
subval[11] = new Array('20','双数','12','=12')
subval[12] = new Array('20','单数','13','=13')
subval[13] = new Array('20','双数','14','=14')
subval[14] = new Array('20','单数','15','=15')
subval[15] = new Array('20','双数','16','=16')
subval[16] = new Array('20','单数','17','=17')
subval[17] = new Array('20','双数','18','=18')
subval[18] = new Array('20','单数','19','=19')
subval[19] = new Array('20','双数','20','=20')
function changeselect2()
{
document.form2.s2.length = 0; //清空s2的值
document.form2.s2.options[0] = new Option('==请选择==','');
document.form2.s2.options[1] = new Option('选择单数','单数');
document.form2.s2.options[2] = new Option('选择双数','双数');
document.form2.s3.length = 0;
document.form2.s3.options[0] = new Option('==请选择==','');
}
function changeselect3(sub1,sub2)
{
document.form2.s3.length = 0; //清空s3的值
document.form2.s3.options[0] = new Option('==请选择==','');
for (i=0; i<subval.length; i++)
{
if ((subval[i][0] == sub1) & (subval[i][1] == sub2))
{document.form2.s3.options[document.form2.s3.length] = new Option(subval[i][2], subval[i][3]);}
}
}
//-->
</script>
<form name="form2">
三级联动：
<select name="s1" onChange="changeselect2()">
<option>==请选择==</option>
<option value="10">1-10</option>
<option value="20">11-20</option>
</select>
<select name="s2" onChange="changeselect3(document.form2.s1.value,this.value)">
<option>==请选择==</option>
</select>
<select name="s3" onChange="alert(this.value)">
<option>==请选择==</option>
</select>
</form>
<!-- 三级联动 Over -->
注：上面是原文，下面是我个人的想法。
为了方便自己，我简单的加了两行注释，也不知道对不对，希望大家不吝赐教。