Ok, this is very rudimentary, but consider this page:
<html>
<head>
<script type="text/javascript">
function parseState()
{
var q = unescape(location.search);
q = q.substring(7, q.length);
if (q != "")
{
document.getElementById("state").options.selectedIndex = q;
}
}
</script>
</head>
<body onload="parseState();">
<form>
<select id="state">
<option value="" selected="selected">Select a State</option>
<option value="AL">Alabama</option>
<option value="AK">Alaska</option>
<option value="AZ">Arizona</option>
<option value="AR">Arkansas</option>
<option value="CA">California</option>
<option value="CO">Colorado</option>
<option value="CT">Connecticut</option>
<option value="DE">Delaware</option>
<option value="DC">District Of Columbia</option>
<option value="FL">Florida</option>
<option value="GA">Georgia</option>
<option value="HI">Hawaii</option>
<option value="ID">Idaho</option>
<option value="IL">Illinois</option>
<option value="IN">Indiana</option>
<option value="IA">Iowa</option>
<option value="KS">Kansas</option>
<option value="KY">Kentucky</option>
<option value="LA">Louisiana</option>
<option value="ME">Maine</option>
<option value="MD">Maryland</option>
<option value="MA">Massachusetts</option>
<option value="MI">Michigan</option>
<option value="MN">Minnesota</option>
<option value="MS">Mississippi</option>
<option value="MO">Missouri</option>
<option value="MT">Montana</option>
<option value="NE">Nebraska</option>
<option value="NV">Nevada</option>
<option value="NH">New Hampshire</option>
<option value="NJ">New Jersey</option>
<option value="NM">New Mexico</option>
<option value="NY">New York</option>
<option value="NC">North Carolina</option>
<option value="ND">North Dakota</option>
<option value="OH">Ohio</option>
<option value="OK">Oklahoma</option>
<option value="OR">Oregon</option>
<option value="PA">Pennsylvania</option>
<option value="RI">Rhode Island</option>
<option value="SC">South Carolina</option>
<option value="SD">South Dakota</option>
<option value="TN">Tennessee</option>
<option value="TX">Texas</option>
<option value="UT">Utah</option>
<option value="VT">Vermont</option>
<option value="VA">Virginia</option>
<option value="WA">Washington</option>
<option value="WV">West Virginia</option>
<option value="WI">Wisconsin</option>
<option value="WY">Wyoming</option>
</select>
</form>
</body>
</html>
If this page was named "pickstate.html", and you loaded it with the querystring:
pickstate.html?state=1
Then, "Alaska" would be selected in the SELECT element.
Why do I say it's rudimentary? For one, the querystring parser isn't robust. Ideally, you'd parse the entire querystring into a JavaScript array, so you could pass in multiple values. Not important in your scenario. Also, it relies on "?state=" having seven characters, intead of finding the value by searching for the equal sign.
Next, the index has no association with the actual value. I would create an array of state names, and instead of passing in the INDEX, I would pass in the two letter state value. I would DERIVE the index by finding the state abbreviation in the array.
But the point was to show you the mechanism. It doesn't matter if the SELECT element is built via an external JavaScript, as long as it is rendered onto the page.
