JavaScript - any way to cancel SELECT onChange

i have a SELECT box and i have JS wired to the onChange event.
for example, suppose my select has 2 options  {A,B,C,D}.
Is this possible:
if the user currently has A selected, when they select B, is it possible to cancel the change and revert back to A?

Once u get the value in the on change event get the index of the value for which u want to be selected like in ur case now is A so get the index of that and change the selected index to = to what ever A has...

function fnCheck()
		{
			if(document.Form1.sel1.selectedIndex==0)
			{
			alert("here");
			document.Form1.sel1.selectedIndex=1;
			}
		}
Here I am not allowing the user to select Index 0. And hardcoding it to 1. Instead to go to the last selection, you can store the last selection in a hidden varaiable and always force that value.
Of course you would be displaying a better message than the "here" i have used.

i think if your major concern is also reverting back to the exact value selected then on every selectchange event ,store the selcted value in an hidden element.
so when the user next shifts to an unacceptable value, set the drop down box to the last correct value.