In honor of Telemonian Ajax, apparently

Read Head Rush Ajax yesterday. If you already know Javascript and the DOM, all there is left to learn about the magic of Ajax is the XMLHttpRequest / Msxml2.XMLHTTP / Microsoft.XMLHTTP functions, which aparently all work identically.

/* ajax-http-request.js */
function newHttpRequest() {
  var request = null;
  try {
    request = new XMLHttpRequest();
  } catch (trymicrosoft) {
    try {
      request = new ActiveXObject("Msxml2.XMLHTTP");
    } catch (othermicrosoft) {
      try {
         request = new ActiveXObject("Microsoft.XMLHTTP");
      } catch (failed) {
        request = null;
        }
    }
  }
  return(request);
}

Given that simple library file, you can do this:

/* some-other-javascript-file.js */
var req = newHttpRequest();
if (req == null)
  alert("Error creating request object!");

function dealWithResponse() {
  if (req.readyState == 4) {
    if (req.status == 200)
      doSomethingWith(req.responseText);
    } else {
      throwAnErrorOrSomething();
  }
}
req.open("GET", "someurl", true);
req.onreadystatechange = dealWithResponse;
req.send(null);

And that's all you really need to know to do Ajax.