javaScript阻止浏览器F5刷新

<script type="text/javascript">
   //禁止用F5键 
   document.onkeydown = function (e) {
     var ev = window.event || e;
     var code = ev.keyCode || ev.which;
     if (code == 116) {
          ev.keyCode ? ev.keyCode = 0 : ev.which = 0;
          cancelBubble = true;
          return false;
     }
   } 
  //禁止右键刷新
  document.oncontextmenu=function(){return false};
</script>