Comments on: XMLHttpRequest and Javascript Closures

By: World Wide Weird

World Wide Weird — Fri, 10 Apr 2009 13:17:19 +0000

Use the with keyword with code blocks that reference the object instead of passing this or self. This even works when, for example, calling the object's methods from setTimeout. :D

By: Anonymous

Anonymous — Thu, 05 Feb 2009 10:25:33 +0000

By: Anonymous

Anonymous — Mon, 15 Jan 2007 19:09:01 +0000

The head of this is strong

my problem is related to the following code

By: Morris Johns

Morris Johns — Sun, 02 Jul 2006 23:24:06 +0000

I wrote an article explaining closures if you are interested:
http://blog.morrisjohns.com/javascript_closures_for_dummies

By: robin

robin — Thu, 02 Feb 2006 09:13:57 +0000

Where the hell has this code gone??!?

By: Widow Maker

Widow Maker — Tue, 30 Nov 1999 00:00:00 +0000

Thanks :)

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

By: sobri

sobri — Tue, 30 Nov 1999 00:00:00 +0000

Just thought I’d mention that XMLHttpRequest is implemented in Safari also.

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

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

By: Carl Smotricz

Carl Smotricz — Tue, 30 Nov 1999 00:00:00 +0000

Thanks for an excellent and very useful writeup!

// 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.

By: HarryF

HarryF — Tue, 30 Nov 1999 00:00:00 +0000

Nice explaination. Many thanks for clearing that one up (and note to self, I should start using Venkman regularily).

By: Bryon Bean

Bryon Bean — Tue, 30 Nov 1999 00:00:00 +0000

-- snip --
// Have to assign "this" to a variable - not sure why can't use directly
var self = this;
-- snip --

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.