JS Shielding keyboard Events

<script>
function KeyDown () {//Mask right mouse button, CTRL + N, SHIFT+F10, F5 refresh, backspace key
Alert ("ASCII code is:" +event.keycode);
if ((Window.event.altKey) &&
((window.event.keycode==37) | |//SHIELD ALT + arrow key ←
(window.event.keycode==39)) ) {//mask ALT + arrow key →
Alert ("Don't use ALT + arrow keys to forward or rewind the page!") ");
Event.returnvalue=false;
}
if ((event.keycode==8) | |//MASK BACKSPACE Delete key
(event.keycode==116) | | Mask F5 Refresh Key
(event.keycode==112) | | Mask F1 Refresh Key
(Event.ctrlkey && event.keycode==82)) {//ctrl + R
event.keycode=0;
Event.returnvalue=false;
Alert ("Don't let you use fast! ");
}
if ((Event.ctrlkey) && (event.keycode==78))//Shielded CTRL + N
{
Alert ("CTRL + N");
Event.returnvalue=false;
}
if ((Event.shiftkey) && (event.keycode==121))//shielded SHIFT+F10
{
Alert ("Shift+f10");
Event.returnvalue=false;
}
if (Window.event.srcElement.tagName = = "A" && Window.event.shiftKey)
{
Window.event.returnValue = false; Screen shift and left mouse button to open a new page
}

if ((Window.event.altKey) && (window.event.keycode==115)) {//shielded ALT+F4
Alert (' Alt+f4 ');
Window.showmodelessdialog ("About:blank", "" "," dialogwidth:1px;dialogheight:1px ");
return false;
}
}
Document.onkeydown = KeyDown
</script>