Need help finding a simple Javascript code.

var form = $('#yourformid');
var select1 = $('#your1stselectid');
var select2 = $('#your2ndselectid');

var options = {
  japan: ['Toyota','Honda','Nissan'],
  american: ['Ford','Chevy','Cadillac']
};

select1.change(function() {
   if (undefined != options[this.value]) {
      select2.children().remove();
      $.each(options[this.value],function(car) {
         $('option', {
            name: car.toLowerCase(),
            value: car
         }).appentTo(select2);
      });
   }
});

<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<title>example</title>
<script type="text/javascript">

groups = [
//	 id   name
	["0", "Japanese Cars"],
	["1", "American Cars"]	//please note, that you don't need a comma in this line (last)
];

cars = [
//	 name1     name2    name3 ...
	["Toyota", "Honda", "Nissan"],	//0
	["Ford", "Chevy", "Cadillac"]	//1
];

function _e(objID)
{
	return document.getElementById(objID);
}

function clearSelect(select)
{
	for (var i=select.options.length-1; i >= 0; i--)
	{
		select.remove(i);
	}
}

function addSelectOption(parent, text, value)
{
	var newOption = document.createElement("option");
	newOption.appendChild(document.createTextNode(text));
	newOption.setAttribute("value", value);

	parent.appendChild(newOption);
}

function buildGroupsList()
{
	var s = _e('group');
	clearSelect(s);

	for (var i=0; i<groups.length; i++)
	{
		addSelectOption(s, groups[i][1], groups[i][0]);
	}
}

function buildCarsList()
{
	var group = _e('group').value;
	var s = _e('car');
	clearSelect(s);

	for (var i=0; i<cars[group].length; i++)
	{
		addSelectOption(s, cars[group][i], cars[group][i]);
	}

}

function initForm()
{
	buildGroupsList();
	buildCarsList();
}

</script>
</head>

<body onLoad="initForm();">

<form name="example" id="example" action="" method="post">

<select id="group" name="group" onChange="buildCarsList()">
</select><br />
<select id="car" name="car">
</select><br />
<input type="submit" value="submit!">

</form>
</body>
</html>