n级联动下拉菜单

<form name="isc">
<table border="0" cellspacing="0" cellpadding="0">
<tr align="center">
<td nowrap height="11">  

<select name="example" size="1" onchange="redirect(this.options.selectedindex)">
<option selected>---select1-------------</option>
<option>webmaster sites</option>
<option>news sites</option>
</select>

<select name="stage2" size="1" onchange="redirect1(this.options.selectedindex)">
<option value=" " selected> </option>
<option value=" " selected>---select2--------------</option>
<option value=" " selected>---select2--------------</option>
</select>

<select name="stage3" size="1" onchange="redirect2(this.options.selectedindex)">
<option value=" " selected> </option>
<option value=" " selected>---select3----------------</option>
<option value=" " selected>---select3----------------</option>
</select>

<script>
<!--

/*
triple combo script credit
by hamid cheheltani/ website abstraction (http://www.wsabstract.com)
visit <a href="http://wsabstract.com" target=_blank>wsabstract.com</a> for this and over 400+ other scripts
*/

var groups=document.isc.example.options.length
var group=new array(groups)
for (i=0; i<groups; i++)
group[i]=new array()

group[0][0]=new option("---select2---"," ");

group[1][0]=new option("now select this one"," ");
group[1][1]=new option("javascript","47");
group[1][2]=new option("dhtml","46");
group[1][3]=new option("cgi","45");

group[2][0]=new option("now select this one"," ");
group[2][1]=new option("general news","115");
group[2][2]=new option("technology news","116");

var temp=document.isc.stage2


function redirect(x){
for (m=temp.options.length-1;m>0;m--)
temp.options[m]=null
for (i=0;i<group[x].length;i++){
temp.options[i]=new option(group[x][i].text,group[x][i].value)
}
temp.options[0].selected=true
redirect1(0)
}



var secondgroups=document.isc.stage2.options.length
var secondgroup=new array(groups)
for (i=0; i<groups; i++) {
secondgroup[i]=new array(group[i].length)
for (j=0; j<group[i].length; j++) {
secondgroup[i][j]=new array() }}

secondgroup[0][0][0]=new option("---select 3---"," ");
secondgroup[1][0][0]=new option("---select 3---"," ");
secondgroup[1][1][0]=new option("now select this one"," ");
secondgroup[1][1][1]=new option("website abstraction","http://wsabstract.com");
secondgroup[1][1][2]=new option("javascript for the non programmer","http://webteacher.com/javascript/");
secondgroup[1][1][3]=new option("java-scripts.net","http://java-scripts.net");

secondgroup[1][2][0]=new option("now select this one"," ");
secondgroup[1][2][1]=new option("dynamic drive","http://www.dynamicdrive.com");
secondgroup[1][2][2]=new option("beginner/'s guide to dhtml","http://www.geocities.com/researchtriangle/facility/4490/");
secondgroup[1][2][3]=new option("web coder","http://webcoder.com/");

secondgroup[1][3][0]=new option("now select this one"," ");
secondgroup[1][3][1]=new option("cgi resources","http://www.cgi-resources.com");
secondgroup[1][3][2]=new option("ada/'s intro to cgi","http://adashimar.hypermart.net/");

secondgroup[2][0][0]=new option("---select 3---"," ");
secondgroup[2][1][0]=new option("now select this one"," ");
secondgroup[2][1][1]=new option("cnn","http://www.cnn.com");
secondgroup[2][1][2]=new option("msnbc","http://www.msnbc.com");
secondgroup[2][1][3]=new option("abc news","http://www.abcnews.com");

secondgroup[2][2][0]=new option("now select a page"," ");
secondgroup[2][2][1]=new option("news.com","http://www.news.com");
secondgroup[2][2][2]=new option("wired","http://www.wired.com");

var temp1=document.isc.stage3
function redirect1(y){
for (m=temp1.options.length-1;m>0;m--)
temp1.options[m]=null
for (i=0;i<secondgroup[document.isc.example.options.selectedindex][y].length;i++){
temp1.options[i]=new option(secondgroup[document.isc.example.options.selectedindex][y][i].text,secondgroup[document.isc.example.options.selectedindex][y][i].value)
}
temp1.options[0].selected=true
}

function redirect2(z){
window.location=temp1[z].value
}

//-->
</script>

  </td>
</tr>
</table>
</form>

<p><font face="arial" size="-2">this free script provided by</font><br>
<font face="arial, helvetica" size="-2"><a href="http://wsabstract.com">website
abstraction</a></font></p>