怎样屏蔽浏览器关闭按钮及ALT+F4 快捷键

 1<script>   
 2function KeyDown(){ //屏蔽鼠标右键、Ctrl+n、shift+F10、F5刷新、退格键   
 3//alert("ASCII代码是："+event.keyCode);   
 4if ((window.event.altKey)&&   
 5((window.event.keyCode==37)|| //屏蔽 Alt+ 方向键 ←   
 6(window.event.keyCode==39))){ //屏蔽 Alt+ 方向键 →   
 7alert("不准你使用ALT+方向键前进或后退网页！");   
 8event.returnValue=false;   
 9}   
10if ((event.keyCode==8) || //屏蔽退格删除键   
11(event.keyCode==116)|| //屏蔽 F5 刷新键   
12(event.keyCode==112)|| //屏蔽 F1 刷新键   
13(event.ctrlKey && event.keyCode==82)){ //Ctrl + R   
14event.keyCode=0;   
15event.returnValue=false;   
16}   
17if ((event.ctrlKey)&&(event.keyCode==78)) //屏蔽 Ctrl+n   
18event.returnValue=false;   
19if ((event.shiftKey)&&(event.keyCode==121)) //屏蔽 shift+F10   
20event.returnValue=false;   
21if (window.event.srcElement.tagName == "A" && window.event.shiftKey)   
22window.event.returnValue = false; //屏蔽 shift 加鼠标左键新开一网页   
23if ((window.event.altKey)&&(window.event.keyCode==115)){ //屏蔽Alt+F4   
24window.showModelessDialog("about:blank","","dialogWidth:1px;dialogheight:1px");   
25return false;}   
26}   
27function Showhelp(){   
28alert("Wrong!");   
29return false;   
30}   
31</script>