Pluggable business logic

Not all of our business logic needs to live inside our components, encapsulated from the outside world. Instead, it would be ideal if we could write our business logic as a set of functions. In theory, this provides us with a clear separation of concerns. The components are there to deal with the specific architectural concerns that help us scale, and the business logic can be plugged into any component. In practice, excising business logic from components isn't trivial.

Extending versus configuring

There are two approaches we can take when it comes to building our components. As a starting point, we have the tools provided by our libraries and frameworks. From there, we can keep extending these tools, getting more specific as we drill deeper and deeper into our features. Alternatively, we can provide our component instances with configuration values. These instruct the component on how to behave.

The advantage of extending things that would otherwise need to be configured...