JavaScript Function to Detect a DropdownListItem

I have one TextBox say txtBox1 followed by a DropdownList --ddl1 and another textBox2 below that.
Now the user types a name into textBox1 and then selects one Item from the dropdown list.Now if the selected dropdownItem's index is 2 I want to copy textBox1.Text to TextBox2.Text. other wise TextBox2.text is to be cleared.

Can some one urgently help me with a javascript function to do this ?Iam using asp.net with VB.net coding

Go to the html view, and in the head put this:

<script type="text/javascript">
function moveText(drop, index)
{
var oDrop = document.getElementById(drop);
var txt1 = document.getElementById('TextBox1');
var txt2 = document.getElementById('TextBox2');
if(oDrop.selectedIndex == index)
{
txt2.value = txt1.value;
}
else
{
txt2.value = '';
}

}
</script>

And now in your vb code you'll have to add the event, so in the page load put this:

ddl1.Attributes.Add("onChange", "moveText('ddl1', '2')")