js禁止页面刷新&后退

<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;      }      //下面代码实现全屏显示      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>