getElementById.contentDocument error in IE

<html>
   <script type="text/javascript">
      function func() {
         alert(document.getElementById('iView').contentDocument);
      }    
   </script>
   <body>
      <iframe id="iView" style="width:200px;height:200px;"></iframe>
      <a href="#" onclick="func();">click</a>
   </body>
</html>

After click, Firefox returns [object HTMLDocument]. Internet Explorer returns undefined.

How can I select the iView element with Internet Explorer? Thanks.