function GetXmlHttpObject()
{
if (window.ActiveXObject)
  {
  // code for IE6, IE5
  return new ActiveXObject("Microsoft.XMLHTTP");
  }
if (window.XMLHttpRequest)
  {
  // code for IE7+, Firefox, Chrome, Opera, Safari
  return new XMLHttpRequest();
  }
return null;
}

function GetFile(page)
{
  var xmlhttp = GetXmlHttpObject();
  this.url1="cos.txt";
  this.url2="about.txt";
  this.url3="test2.txt";
  this.url4="contact.txt";
  this.url5="control.txt";
  this.url6="brochure.txt";
  this.url7="warranty.txt";
  var mstrUrl = "url"+page;
  xmlhttp.onreadystatechange = function(){
          if (xmlhttp.readyState==4)
              {
              document.getElementById('mainContent').innerHTML = xmlhttp.responseText;
              }
  }
  xmlhttp.open("GET",this[mstrUrl],true);
  xmlhttp.send(null);
}