屏蔽F1~F12的快捷键的js函数

function window.onhelp(){return false} //屏蔽F1帮助 
/*keyCod从113-123分别禁用了F2-F12键,13禁用了回车键(Enter),8禁用了退格键(BackSpace)*/ document.onkeydown = function(){ 
if(window.event && window.event.keyCode == 113) { 
window.event.keyCode = 505; 
} 
if(window.event && window.event.keyCode == 114) { 
window.event.keyCode = 505; 
} 
if(window.event && window.event.keyCode == 115) { 
window.event.keyCode = 505; 
} 
if(window.event && window.event.keyCode == 116) { 
window.event.keyCode = 505; 
} 
if(window.event && window.event.keyCode == 117) { 
window.event.keyCode = 505; 
} 
if(window.event && window.event.keyCode == 118) { 
window.event.keyCode = 505; 
} 
if(window.event && window.event.keyCode == 119) { 
window.event.keyCode = 505; 
} 
if(window.event && window.event.keyCode == 120) { 
window.event.keyCode = 505; 
} 
if(window.event && window.event.keyCode == 121) { 
window.event.keyCode = 505; 
} 
if(window.event && window.event.keyCode == 122) { 
window.event.keyCode = 505; 
} 
if(window.event && window.event.keyCode == 123) { 
window.event.keyCode = 505; 
} 
if(window.event && window.event.keyCode == 13) { 
window.event.keyCode = 505; 
} 
if(window.event && window.event.keyCode == 8) { 
alert(str+"\n请使用Del键进行字符的删除操作！"); 
window.event.returnValue=false; 
} 
if(window.event && window.event.keyCode == 505){ 

alert(str) 
window.event.returnValue=false; 
} 
}