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;   }//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>