Mastering Modular JavaScript

Chapter 3. Module Design

Thinking in terms of API-driven and documentation-driven design will yield more usable modules than not doing so. You might argue that internals are not that important: “as long as the interface holds, we can put anything we want in the mix!” A usable interface is only one side of the equation; it will do little to keep the maintainability of your applications in check. Properly designed module internals help keep our code readable and its intent clear. In this chapter, we’ll debate about what it takes to write modules with scalability in mind but without getting too far ahead of our current requirements. We’ll discuss the CRUST constraints in more depth, and finally elaborate on how to prune modules as they become larger and more complex over time.

3.1 Growing a Module

Small, single-purpose functions are the lifeblood of clean module design. Purpose-built functions scale well because they introduce little organizational complexity into the module they belong to, even when that module grows to 500 lines of code. Small functions are not necessarily less powerful than large functions, but their power lies in composition.

Suppose that instead of implementing a single function with 100 lines of code, we break it up into three or more smaller functions. We might later be able to reuse one of those smaller functions somewhere else in our module, or it might prove a useful addition to its public interface.

In this chapter, we’ll discuss design considerations ...