function alphanumeric(evt) {
        var theEvent = evt || window.event;
        var key = theEvent.keyCode || theEvent.which;
        key = String.fromCharCode( key );
        var regex = /[^a-zA-Z0-9]/;
        if( regex.test(key) ) {
            theEvent.returnValue = false;
            if(theEvent.preventDefault) theEvent.preventDefault();
        }
    }