On 1/3/11, Mark McDonnell <[email protected]> wrote:
> I've been reading through Stoyan Stefanov's latest book "JavaScript
> Patterns" and was interested to know who here has used the Observer design
> pattern and could you provide some examples of how you had used it.
>
>
> Here is a link to the example provided in the book:
> https://gist.github.com/763762
>
>
> At the moment it seems like I have 'a solution looking for a problem'. I can
> see that this pattern could be quite useful with a more advanced JavaScript
> application (being the event driven nature of JavaScript) but I'm not sure
> what scenario I would use or could use such a pattern?
>
Sure.
I use the pattern quite a bit. I learned the approach by Dan
Steinman's Dynamic Duo, before I knew the words "Observer" or
"pubsub".
What Dan did is use a decorator or "wrapper" object: DynLayer. A
DynLayer object's prototype had adapter methods for IE DOM and NS dom,
as well as methods that weren't available on DIV or LAYER elements
(LAYER was an NS4 element that had many problems).
The DynLayer object itself could be extended to such thins as the
famous draggable "Flower Pot".
Custom events on the DynLayer were implemented as functions on the
prototype. ECMAScript "[[Put]]" works by adding or changing a property
to the instance, and [[Get]] works by looking on the instance and then
up the prototype chain.
So the DynLayer prototype woul have something like:
DynLayer.prototype.onshow = function(){};
And then when you called "show()", the onshow would be called. But you
could shadow that "onshow" by adding an "onshow" callback to the
object.
myLayer.onshow = function() {
alert("I'm shown!");
};
The downside there was that at most one function call would be
hard-wired to the event.
This is fixable, of course, but with a lot more work. I explained my
own solution to the problem here:
http://dhtmlkitchen.com/?category=/uncategorized/&date=2008/01/04/&entry=Event-Notification-System
That explains how I copied the DOM events model for handling errors in
event callbacks.
I use this for quite a lot of stuff. Most recently, TestReporter want
to know when TestRunner fires "oncomplete" so that it can show the
results. That design may change so that it logs things continually,
allowing for continuous communication. But the point is about
communication here. TestRunner just sends a message "I'm Done".
comp.object poster H.S. Lahman has also good explanations about "I'm Done".
[...]
>
> I know this is a bit of an odd request, but really I'm just interested to
> know what 'real world' examples there are using this pattern so I can get a
> better idea (when the time comes) how I can use it.
>
Panel onshow, For Ajax stuff I use it a lot. I create an Ajax request
wrapper and multiple subscribers may subscribe to "complete",
"success", "failure", etc.
--
Garrett
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