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Design Patterns in Javascript – Model-View-Controller

Model-View-Controller, or MVC for short, is an software architecture pattern for user interfaces that creates a distinction between the display (or view), the data (or model), and the interaction (or controller). In this article, I'm going to focus specifically on how MVC applies to the client side of web applications. What I mean is that MVC in a web based ui translates to

This separation of concerns means that as long as the model stays consistent, you can

  1. Create multiple views for the same model
  2. Develop the controller and views independently

For a great example of 1 checkout css Zen Garden. Here, the same HTML (the model) can be seen with many different views.

Now checkout the jquery ui demos for a clear example of both 1 and 2. Again, the same HTML has many different views with the various CSS themes, and you can also see jquery ui controller code in action. The Javascript manipulates the model, affecting what you see and how you see it, independently of which theme (or view) you choose.

What this all means is that you can create semantically correct HTML optimized for search engines, CSS so your page looks good for humans, and Javascript to make your page interactive. In other words, content can be separated from presentation, which can be separated from the interaction behavior. The CSS and Javascript can be developed (mostly) independently and only be loosely coupled to the HTML.

Taking this a step further, it's possible to create generic views and controllers using CSS and Javascript that work on a small generic model. jquery ThickBox is an example of this, since it can be used on any page where you have <a class='thickbox' ...>...</a>. As long as your HTML supports the generic model, you can reuse the CSS and Javascript across multiple pages.


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Programming as Design

Some say programming is engineering, others call it an art. A few might (mistakenly) think it's a science. But both the art and engineering can be encapsulated under the umbrella of design. The best design is functional art, and a huge part of the artistic beauty of a product is a result of carefully engineered functionality. Products that are not carefully designed and engineered generally suck to use, and that applies to everything from cameras to software APIs.

Design Principles

There are 4 major principles of graphic design.

  1. alignment
  2. proximity
  3. contrast
  4. consistency / repetition


The principle of alignment is that everything on a page should be connected to something else on the page. The goal of alignment in graphic design is to create visual associations, often using a grid based layout. In software, we can apply this principle to the connectedness of data, such as the object inheritance hierarchy and relational data structures. Ideally, all your objects fit nicely into a well-defined hierarchy and your data structures relate to each other in an intuitive fashion. Of course, the real world of programming is never as clean as you'd like, but keep this principle in mind whenever you create a new object, add a new dependency, or modify relational structures.

  • Does the object cleanly fit within the existing hierarchy? If not, do you need to change the new object, or re-align the hierarchy?
  • How does this data structure relate to that other data structure? What will happen if the relations change? Will you need to re-align the relational structures?

Keeping your objects and data structures neatly aligned will result in easier to understand relations and hierarchies.


The principle of proximity is that related items should be grouped together. Grouping things together is simple way to show relatedness. In software development, that generally means putting related functions into the same module, and related modules into the same package. Helper functions should be located near the functions that call them. Basically, group blocks of code in a logically consistent manner. And if possible, put documentation and tests close to the code too (python's doctest module provides a great way to do that). One of the major benefits of following this principle is that it reduces the amount of time you'll spend searching thru and understanding your own code. If all your code is organized in logical groups, and related functions are near each other in the same file, then it's much easier to find a particular block of code.


The principle of contrast is that if two things are not the same, then make them very different. The goal with contrast is to make different things distinctive from each other. Naming is great place to apply this principle. Names are all you have to distinguish between objects, functions, variables, and modules, so make sure that your names are distinctive and descriptive. Good names can tell you exactly what something is, and even imply its properties and behavior. Use different naming styles for different types of things. Private variables could be prefixed with an underscore, like _private, versus public variables like public, and CamelCase class names, as in MyClassName. Having a distinctive naming style lets you know at a glance whether something is a class, variable, or function, making your code much more readable. Whatever naming style you choose, use it consistently.


The principle of consistency, or repetition, is that you repeat design elements. Repetition helps patterns become internalized and instantly recognizable. For programming, that means keeping a consistent code style, with consistent naming practices. Also, try to use well known standard conventions and protocols, shared libraries, and design patterns. Your code should make sense, or at least be readable, to those familiar with the language and domain. You're not just writing code for yourself, you might be writing code for other programmers, maybe your manager, but most importantly, you're writing code for your future self. It always sucks coming back to code you haven't touched in months and not knowing what the hell is going on. Consistent style and software design can save you from that headache.

Programming as Design

If all this seems like obvious common sense to you, then great! But common sense isn't always so common. The point of this article is make you aware that everyday software programming is filled with design choices. Naming a variable is a design choice. Creating a new module is a design choice. The layout of your working directory is a design choice. Be conscious of these choices and use the above principles and to inform your decisions. The choices you make communicate how the software works and how the code fits together. Make every choice deliberate and justifiable. Use refactoring to improve the design without affecting the functionality.

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