Identifying A Selected Option By Its Position?

I have a simple form with an options drop down box:

<form method="POST" name="form">
<select autocomplete="off" id="input" name="input" onchange="this.form.submit();goHere();">
<option>Choose...</option>

[code]....

I wish to identify the option chosen in the function but not by its value, by its position:

<script>
function goHere(){
var s = document.getElementById("input");

[code]....

I was hoping that variable "u" would be either 0, 1, 2, or 3.How can I get a variable to alert me the position of the selected option in the form? I think it is elements[i].