Asynchronous Response

• Pass true as third argument to open().
• Set event handler on onreadystatechange property.

var request = HTTP.newRequest();

//Register event handler
request.onreadystatechange = function() {
   if (request.readyState == 4) { //if request is finished
      if (request.status == 200) // if it was successful
       alert(request.responseText);
   }
}

request.open("GET", url);

request.send(null);

• During long downloads Firefox calls it with readyState == 3 many times, but IE does it only once.