Comments on: Singletons and Event Arbiters

By: Aaron N.

Aaron N. — Mon, 13 Jul 2009 16:01:02 +0000

@Kris very clever!

By: Kris Wallsmith

Kris Wallsmith — Mon, 13 Jul 2009 04:14:21 +0000

I’ve been using Class.Occlude and occluding to document.body when I need a singleton. Works like a charm.

By: Aaron N.

Aaron N. — Thu, 02 Jul 2009 20:48:26 +0000

You have the $lambda stuff correct, yes.

By: Pete Duncanson

Pete Duncanson — Thu, 02 Jul 2009 13:22:44 +0000

@Andy – you could do it in JS but you have to use a function to return the value. You could do it just as a variable but an mistyped variable can return null which might still get through your code, calling a non-existant function via a typo though throw an error.

var MyEventNames = {
login = function() { return “login”; },
logout = function() { return “logout”; } )
}

mySite.fireEvent( myEventNames.login() );

I’m not sure if you can do the same using the $lambda function guess you could as thats what its for which would make it more readable but I’ve not used lambda much yet so could not comment but I guess it would look like this:

var MyEventNames = {
login = $lambda( “login” ),
logout = $lambda( “logout” )
}

@ anyone – Is the $lambda stuff right?

By: Benoit

Benoit — Thu, 25 Jun 2009 09:37:58 +0000

Great way of starting up an application, I like the mootools event system over many other frameworks.

Andy, I totally agree with you, but its true javascript doesn’t has defines or constants.

Altough you could use centralized config object to handle that sort of text keys & constants, what I’ve done in many projects. We use a config class with getters an setters for storing app constants as other various parameters (urls, etc.). We access it ine with something like this Config.get(‘LoginEventName’).
Our object throws errors when calling undefined config key, so we are aware of typo mistakes.
Of course you can use the singleton pattern for this if you want.

By: Aaron N.

Aaron N. — Wed, 24 Jun 2009 23:21:39 +0000

Ah, well, JavaScript just doesn’t work this way. I’m not going to go into details here (it would be a long comment, for sure), but this kind of #define functionality just doesn’t exist for JavaScript (in large part because it doesn’t have a compiler – at least not in the sense that C/C++ does).

By: Andy

Andy — Wed, 24 Jun 2009 22:54:27 +0000

Only that whenever you have multiple uses of the same string somewhere, then it becomes easy to misspell on of them, of if for some reason you want to change the string due to change in functionality that would require a rename, it means you can just change it in one place, instead of multiple places. If you added a new page to your website, and typed ‘logn’ instead, how long would it take to notice find the issue?
In C/C++, if you misspelled the #define you would get a compile time error, which means that the error would be caught much earlier ( and cheaper). One way of thinking about it is this. Say you had an event called ‘login’ that was used in 7 different files, and multiple times in some files. When you add a new openID login as well,you decide to rename the old ‘login’ event to ‘loginPassword’. Would you prefer to change it in one place, or in multiple places ? Over the years I’ve lost count the number of times things like this changed in 6 of the files, but for whatever reason the 7th file was missed.

By: Aaron N.

Aaron N. — Wed, 24 Jun 2009 21:05:59 +0000

This is just an example. This isn’t taken from real code I’ve authored – I just tried to think of a really simple way to illustrate the point. Given that I am NOT a C/C++ guy, what is it about ‘login’ that you find so distasteful?

By: Andy

Andy — Wed, 24 Jun 2009 20:53:23 +0000

I like it :). However, as an old time C/C++ guy, I’ve got lots of red flags about the use of strings like ‘login’ in multiple places. I would normally handle this in C by using a #define. Whats the best way of handling the same thing in Javascript ?

By: davidck

davidck — Wed, 24 Jun 2009 14:16:32 +0000

Ooo, this is good (Event Arbiters). I’ve always been passing an instance of an object A to communicate with object B. The fact that modularity is improved will make widgets more re-usable.