如何用javascript获取剪贴板内容

Question

据说这段代码可以，但第一句就没法通过，any help appreciate
netscape.security.PrivilegeManager.enablePrivilege('UniversalXPConnect');
      var clip = Components.classes['@mozilla.org/widget/clipboard;1'].createInstance(Components.interfaces.nsIClipboard);
      if (!clip) return;
      var trans = Components.classes['@mozilla.org/widget/transferable;1'].createInstance(Components.interfaces.nsITransferable);
      if (!trans) return;
      trans.addDataFlavor('text/unicode');
      clip.getData(trans,clip.kGlobalClipboard);
      var str = new Object();
      var len = new Object();
      try {
         trans.getTransferData('text/unicode',str,len);
      }
      catch(error) {
         return null;
      }
      if (str) {
         if (Components.interfaces.nsISupportsWString) str=str.value.QueryInterface(Components.interfaces.nsISupportsWString);
         else if (Components.interfaces.nsISupportsString) str=str.value.QueryInterface(Components.interfaces.nsISupportsString);
         else str = null;
      }
      if (str) {
         return(str.data.substring(0,len.value / 2));
      }