运用 JS javascript 禁止刷新 前进 后退

<script language="Javascript"><!--
function document.oncontextmenu(){event.returnValue=false;}//屏蔽鼠标右键
function window.onhelp(){return false} //屏蔽F1帮助
function document.onkeydown()
{
? if ((window.event.altKey)&&
????? ((window.event.keyCode==37)||?? //屏蔽 Alt+ 方向键 ←
?????? (window.event.keyCode==39)))?? //屏蔽 Alt+ 方向键 →
? {
???? alert("不准你使用ALT+方向键前进或后退网页！");
???? event.returnValue=false;
? }?
?????? if ((event.keyCode==8)? ||???????????????? //屏蔽退格删除键
????? (event.keyCode==116)||???????????????? //屏蔽 F5 刷新键
????? (event.ctrlKey && event.keyCode==82)){ //Ctrl + R
???? event.keyCode=0;
???? event.returnValue=false;
???? }
? if (event.keyCode==122){event.keyCode=0;event.returnValue=false;}? //屏蔽F11
? if (event.ctrlKey && event.keyCode==78) event.returnValue=false;?? //屏蔽 Ctrl+n
? if (event.shiftKey && event.keyCode==121)event.returnValue=false;? //屏蔽 shift+F10
? if (window.event.srcElement.tagName == "A" && window.event.shiftKey)?
????? window.event.returnValue = false;???????????? //屏蔽 shift 加鼠标左键新开一网页
? if ((window.event.altKey)&&(window.event.keyCode==115))???????????? //屏蔽Alt+F4
? {
????? window.showModelessDialog("about:blank","","dialogWidth:1px;dialogheight:1px");
????? return false;
? }
}
</script>