Javascript 'Disable F5 to avoid refresh my key down windows event

<script>
window.history.forward(1);
document.attachEvent("onkeydown", my_onkeydown_handler);
function my_onkeydown_handler()
{
switch (event.keyCode)
{

case 116 : // 'F5'
event.returnValue = false;
event.keyCode = 0;
window.status = "We have disabled F5";
break;
}
}
</script>