As a program grows in size it's important to split it into
modules, so that you don't need to understand all of it to make a
small modification. Often these modules can be supplied by
different teams and combined dynamically. In this refactoring
essay I split a small program using Presentation-Domain-Data
layering. I then refactor the dependencies between these modules
to introduce the Service Locator and Dependency Injection
patterns. These apply in different languages, yet look different,
so I show these refactorings in both Java and a classless
JavaScript style.