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;
}
}