my problem is related to the following code

You approached this subject a wee while back in the Advanced PHP Forums, and keeping the topic in focus is great :)

http://developer.apple.com/internet/webcontent/xmlhttpreq.html

I’m not sure of its status in Opera, but I’m hoping for the best :)

// Have to assign “this” to a variable - not sure why can’t use directly
var self = this;

I’ve been struggling with this for days! The answer is that “this” is the context of the function/object definition (i.e. HTTPClient) at the time the constructor runs (i.e. at “new” time) but the context of the call when a callback occurs; i.e. when StateChangeCallBack() is called, this points inside some completely different object. Venkman (many Kudos to the Moz team for Venkman!) shows this quite nicely as you stumble through errors and exceptions.

This is where JavaScript closure comes in: A function “remembers” the context it was defined in, including all variables (except “this”, of course!) So when your callback runs, the “self” it refers to is the very “self” that was pointed at “this” at the time of creation of HTTPClient.

After reading you article I just happend to stumble on this information, thought you might enjoy…

(From http://www.crockford.com/javascript/private.html):

function Container(param) {

function dec() {
if (secret > 0) {
secret -= 1;
return true;
} else {
return false;
}
}

this.member = param;
var secret = 3;
var self = this;
}

…

By convention, we make a private self parameter. This is used to make the object available to the private methods. This is a workaround for an error in the ECMAScript Language Specification which causes this to be set incorrectly for inner functions.