As today’s web applications continue to evolve and get more complex, it has become a lot more commonplace to keep a data model present inside of your javascript. You would then write various widgets, modules, or whatever that would get their data from the model, rather than querying some other web service independently (and if you aren’t doing this, you should!). While centralizing all your data into a nice, organized model that different parts of your code can access, it’s often a challenge to integrate an efficient way to notify the code that depends on these models when the stored data is updated. Lucky for us, Ryan Johnson has created a surprisingly small library that will allow our data model to notify anything that depends on it that it has updated (or loaded, or whatever you’d like in fact).

Before we dig in to the notifications, let’s do a little work to set up an example and some assumptions we’ll be operating under for the sake of this article. First, as prototype is my weapon of choice, that’s what we’ll be using. We’ll also be using prototype as Object.Event uses it as well! Now, let’s pretend that we have a website that has some social networking aspect of some kind. We want to display a short list of who’s currently online (say the 6 most recently active people) in some sort of side bar, and perhaps a count of the total members online in a footer element. Rather than having both these elements poll the server at some interval to update their information, let’s create a little data model that these areas can use instead.
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