js防止按IE按F5刷新

<script language="javascript" type="text/javascript">

    document.onkeydown=function()
    {
        with(window.event)
        {
            if(keyCode == 116)
            {
               keyCode = 0;
         cancelBubble = true;
         return false;
        
            }
        }
    }
</script>