在网页中屏蔽快捷键

<script language="Javascript">  
//屏蔽鼠标右键、Ctrl+N、Shift+F10、F5刷新、退格键  
//屏蔽F1帮助  
function window.onhelp()  
{  
return false  
}  
function KeyDown()  
{  
//alert(event.keyCode);  
//屏蔽 Alt+ 方向键 ← 屏蔽 Alt+ 方向键 →  
if ((window.event.altKey)&&((window.event.keyCode==37)||(window.event.keyCode==39)))  
{  
//alert("不准你使用ALT+方向键前进或后退网页！");  
event.returnValue=false;  
}  
//屏蔽退格删除键,屏蔽 F5 刷新键,Ctrl + R  
if ((event.keyCode==116)||(event.ctrlKey && event.keyCode==82))  
{  
event.keyCode=0;  
event.returnValue=false;  
}  
//屏蔽 Ctrl+n  
if ((event.ctrlKey)&&(event.keyCode==78))  
{  
event.returnValue=false;  
}  
//屏蔽 shift+F10  
if ((event.shiftKey)&&(event.keyCode==121))  
{  
event.returnValue=false;  
}  
//屏蔽 shift 加鼠标左键新开一网页  
if (window.event.srcElement.tagName == "A" && window.event.shiftKey)  
{  
window.event.returnValue = false;  
}  
//屏蔽Alt+F4  
if ((window.event.altKey)&&(window.event.keyCode==115))  
{  
window.showModelessDialog("about:blank","","dialogWidth:1px;dialogheight:1px");  
return false;  
}  
//屏蔽Ctrl+A  
if((event.ctrlKey)&&(event.keyCode==65))  
{  
return false;  
}  
}  
</script>