casecading

//this code from this page

http://www.codingforums.com/showthread.php?t=202456
<html>
<head>

<script type="text/javascript">

var categories = [];categories["startList"] = ["Apparel","Books"]
categories["Apparel"] = ["Men","Women"];
categories["Books"] = ["Biography","Fiction","Nonfiction"];
categories["Men"] = ["Shirts","Ties","Belts"];
categories["Women"] = ["Blouses","Skirts","Scarves"];
categories["Biography"] = ["Contemporay","Historical","Other"];
categories["Fiction"] = ["Science","Romance"];
categories["Nonfiction"] = ["How-To","Travel","Cookbooks"];

var nLists = 3; // number of lists in the set

function fillSelect(currCat,currList){
var step = Number(currList.name.replace(/\D/g,""));
for (i=step; i<nLists+1; i++) {
document.forms[0]['List'+i].length = 1;
document.forms[0]['List'+i].selectedIndex = 0;
}
var nCat = categories[currCat];
for (each in nCat)  {
var nOption = document.createElement('option');
var nData = document.createTextNode(nCat[each]);
nOption.setAttribute('value',nCat[each]);
nOption.appendChild(nData);
currList.appendChild(nOption);
}
}

function getValue(isValue) {
alert(isValue);
}

function init() {
fillSelect('startList',document.forms[0]['List1'])
}

navigator.appName == "Microsoft Internet Explorer" ? attachEvent('onload', init, false) : addEventListener('load', init, false);

</script>
</head>

<body>
<form action="">
<select name='List1' onchange="fillSelect(this.value,this.form['List2'])">
<option selected>Make a selection</option>
</select>
&nbsp;
<select name='List2' onchange="fillSelect(this.value,this.form['List3'])">
<option selected>Make a selection</option>
</select>
&nbsp;
<select name='List3' onchange="getValue(this.value)">
<option selected >Make a selection</option>
</select>
</form>

</body>
</html>