一个三级关联菜单的例子

<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 http://wsabstract.com 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>

原文转自：http://www.ltesting.net