js禁止页面刷新与后退的方法

<script language="javascript">
//禁止用F5键
function document.onkeydown()
{   
 if ( event.keyCode==116)
  {   
    event.keyCode = 0;
    event.cancelBubble = true;
    return false;
  }
}
//禁止右键弹出菜单 
function document.oncontextmenu()
{   
   return false;   
}
//狼蚁网站SEO优化代码实现全屏显示 
function window.onload(){ 
   var Request = new Array();//保存参数 
   var s = location.search.substring(1); 
   if (s && s!=""){ 
    var list = s.split("&");
    for (var i=0; i < list.length; i++){
    var pair = list[i].split("=");
    if (pair[0] && pair[0] !=""){
    Request[unescape(pair[0])] = unescape(pair[1]);
    }
    }
   }
   var fullscreen=Request["fullscreen"];
   if(fullscreen!="yes"){
    var file =self.location;
    var a = window.open("about:blank","","fullscreen=yes");
    self.opener=null;
    self.close();
    a.location=file + "?fullscreen=yes";
   }
}
</script>
<script language="Javascript"><!--
//屏蔽鼠标右键、Ctrl+N、Shift+F10、F11、F5刷新、退格键  
//Author: meizz(梅花雨) 2002-6-18  
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;  
}  
/ 注这还不是真正地屏蔽 Alt+ 方向键， 
因为 Alt+ 方向键弹出警告框时，按住 Alt 键不放， 
用鼠标点掉警告框，这种屏蔽方法就失效了。以后若 
有哪位高手有真正屏蔽 Alt 键的方法，请告知。/  
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>