js禁止页面刷新后退

[javascript]
<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!=""){