用Ajax来控制书签和回退按钮的代码

this is a DOM Element node
      if (currentElement.nodeType == 1) {
         // clear any class name
         currentElement.className = "";
      }                                      
   }

   // cause the new selected menu item to
   // appear differently in the UI
   selectedElement.className = "selected";

   // display the new section in the right-hand
   // side of the screen; determine what
   // our sectionData is

   // display the address book differently by
   // using our local address data we cached
   // earlier
   if (newLocation == "addressbook") {
      // format and display the address book
      sectionData = "<p>Your addressbook:</p>";
      sectionData += "<ul>";

      // fetch the address book from the cache
      // if we don''t have it yet
      if (window.addressBook == undefined) {
         window.addressBook =
               historyStorage.get("addressBook");
      }

      // format the address book for display
      for (var i = 0;
               i < window.addressBook.length;
                     i++) {
         sectionData += "<li>"
                        + window.addressBook[i]
                        + "</li>";                  
      }

      sectionData += "</ul>";
   }

   // If there is no sectionData, then
   // remotely retrieve it; in this example
   // we use fake data for everything but the
   // address book
   if (sectionData == null) {
      // in a real application we would remotely