判断一个页面正在读取中，还没有完全打开

  <div id="loading"> 
    <img src="/Images/indicator_medium.gif" /> 
  </div>
<script type="text/javascript">
    if(document.readyState=="interactive" || document.readyState=="complete"
    || typeof(document.readyState) == "undefined") //firefox
    {
        document.getElementById("loading").style.display = "none";
    }
    </script>