How to Screen Browser Close button and Alt+f4 shortcut keys

button | Browser screen alt+f4 shortcut keys:
<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) | | Shielding ALT + Direction key ←
(window.event.keycode==39))) {//Shielding ALT + Direction key →
Alert ("You are not allowed to use ALT + arrow keys forward or back 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;
}
if ((Event.ctrlkey) && (event.keycode==78))//Shield CTRL + N
Event.returnvalue=false;
if ((Event.shiftkey) && (event.keycode==121))//Shielding SHIFT+F10
Event.returnvalue=false;
if (Window.event.srcElement.tagName = "A" && Window.event.shiftKey)
Window.event.returnValue = false; Screen shift plus left mouse button new page open
if ((Window.event.altKey) && (window.event.keycode==115)) {//Shield ALT+F4
Window.showmodelessdialog ("About:blank", "" "," dialogwidth:1px;dialogheight:1px ");
return false;}
}
function Showhelp () {
Alert ("wrong!");
return false;
}
</script>