phpeveryday.com

A simple version of the code that we will use for cross browser:

// creates XMLHttpRequest Instance
function createXmlHttpRequestObject(){

  // will store XMLHttpRequest object
  // at here
  var xmlHttp;

  // works all exceprt IE6 and older  
  try
  {
  
    // try to create XMLHttpRequest object
    xmlHttp = new XMLHttpRequest();    
  }
  catch(e)
  {
    // assume IE 6 or older
    try
    {
      xmlHttp = new ActiveObject("Microsoft.XMLHttp");
    }
    catch(e){ }
  }
  
  // return object or display error
  if (!xmlHttp)
    alert("Error creating the XMLHttpRequest Object");
  else
    return xmlHttp;
}