var http = createRequestObject();
function createRequestObject() {
   var objAjax;
   var browser = navigator.appName;
   if(browser == "Microsoft Internet Explorer"){
      objAjax = new ActiveXObject("Microsoft.XMLHTTP");
   }else{
      objAjax = new XMLHttpRequest();
   }
   return objAjax;
}

function getNewContent(filname){
   http.open('get',filname);
   http.onreadystatechange = updateNewContent;
   http.send(null);
   return false;
}

function updateNewContent(){
   if(http.readyState == 4){
      document.getElementById('centercontent').innerHTML = http.responseText;
   }
}

function requestIsbnInfo(url) {     
   http.open("GET", url, true);
   http.onreadystatechange = updateNewContent;
   http.send(null);
   return false;
}