pmuellr is Patrick Mueller

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Monday, May 07, 2007

structured javascript

I just listened to the Jon Udell podcast interview with John Lam, which was quite interesting. Highly recommended. I do, of course, have a bone to pick.

At 9:52, the conversation turns to talk about JavaScript. John Lam says JavaScript is "a very difficult language for programming in the medium or the large and by medium and large I'm going to say applications which exceed 5,000 to 10,000 lines of code. Once my JavaScript gets up to that, I have a really hard time maintaining that stuff because modularity is definitely one of the things that isn't really all that well thought out in the JavaScript language. Which is much better in languages like Ruby and Python."

Now, John is certainly correct that JavaScript lacks language level modularity features like namespaces, packages, and class definitions. Typically, a 'class' is defined by creating a constructor function and adding methods to it by adding functions to the constructor's prototype. Packages and namespaces are defined as a top-level objects with the top-level package segment, with a field defined for the next package segment, and then recursing through the remainder of the package segments.

Class definition by running plain old code.

Some JavaScript libraries like YUI and dojo actually do have some code and conventions around defining such things.

So, note that. No language level modularity features like a 'package' and 'class' keyword. It's all dynamic. And perhaps some conventions provided by libraries you happen to be using.

Which is quite similiar to Smalltalk. There are no 'language level' features for defining classes. There is no 'class' keyword. Instead, to define a new class, I'd go into a class browser, and fill in a template like:

    Number subclass: #Fraction
        instanceVariableNames: 'numerator denominator'
        classVariableNames: ''
        poolDictionaries: ''	

This is a class definition. However, literally, it's a message send. A message sent to a class (Number) to create a subclass (Fraction) with two instance variables (numerator and denominator).

I don't recall anyone who ever bothered to learn Smalltalk having made claims that it wasn't modular. So I don't think having language level modularity features is a neccessity for making the language usage modular.

My reference to Smalltalk isn't entirely spurious given the recent news of Dan Ingall's Project Flair. As Tom Waits would 'sing' ... "What's he building in there?".

This leads me to a number of questions:

  • Could we build a set of conventions around package/namespace/class/method definition that would be usable in a number of different contexts? IDEs, live class browsers, etc.

  • What would it mean to build 'images' of code and data in JavaScript? By image I don't mean a .gif file, I mean a collected set of code and data serialized into one or more files. An 'executable unit' for a language interpreter.

  • Could we get these things to work with the rather crude code injection apparatus we currently have for web applications (<script src=...>)?

  • In the unspecified future, we'll have declarative language features in JavaScript. If you'd like to get a taste for what this might look like, right now, look no further than ActionScript 3 from Adobe. Do we want this? Do we need this?

  • WWSD - What Would Self Do? Self is probably the best known prototype-based language. It would be interesting to go back and look at some of the Self stuff; it's been years for me.