This article is in need of a technical review.
This page contains documentation, specific to Mozilla application and add-on developers.
The interface definition: http://mxr.mozilla.org/mozilla-centr...ttpRequest.idl
Using event handlers from native code
(Not sure if it's up-to-date)
From native code, the way to set up onload and onerror handlers is a bit different. Here is a comment from Johnny Stenback <email@example.com>:
The mozilla implementation of nsIXMLHttpRequest implements the interface nsIDOMEventTarget and that's how you're supported to add event listeners. Try something like this: nsCOMPtr<nsIDOMEventTarget> target(do_QueryInterface(myxmlhttpreq)); target->AddEventListener(NS_LITERAL_STRING("load"), mylistener, PR_FALSE) where mylistener is your event listener object that implements the interface nsIDOMEventListener. The 'onload', 'onerror', and 'onreadystatechange' attributes moved to nsIJSXMLHttpRequest, but if you're coding in C++ you should avoid using those.
Though actually, if you use addEventListener from C++ weird things will happen too, since the result will depend on what JS happens to be on the stack when you do it....
Conclusion: Do not use event listeners on XMLHttpRequest from C++, unless you're aware of all the security implications. And then think twice about it.
This is a simple example code for opening a simple HTTP request from a xul application (like a Mozilla extension) without using observers:
var req = Components.classes["@mozilla.org/xmlextras/xmlhttprequest;1"].createInstance(); req.open('POST', "http://www.foo.bar:8080/nietzsche.do", true); req.send('your=data&and=more&stuff=here');