Modules

What Is a Module?

In Morando, a module represents the fundamental unit of work.

Conceptually, a module is a vertical slice that encapsulates a single, well-defined concern of the application. A "vertical slice" means that a module may contain code from all the layers defined for your application, but we will discuss layers in detail in the Layers chapter.

From a technical perspective, a module is simply a folder that follows a defined structure. By convention, module folder names start with a capital letter and contain source code files. Below you can find an example of a User module:

User/
├── UserAvatar.tsx
├── useUser.ts
├── api.ts
└── model.ts

Modules Are Flat

One module folder can't be placed inside another module folder.

That said, modules can contain folders. They cannot be just any folders, and their names are strictly tied to the layers defined in your project. They are layer folders, and to make them easier to tell apart from modules, their names start with a lowercase letter.

We will cover them in the Layers chapter, but for this chapter, it is enough to remember that they are optional. Like modules, layer folders also cannot be nested.

Below is an example of a Shared module that contains utils and components layer folders.

Shared/
├── components/
│   ├── FilterButton.tsx
│   └── ProductIcon.tsx
└── utils/
    ├── getId.ts
    └── getName.ts

Module Dependencies

While modules can't be nested, they can depend on each other. We say that Module A depends on Module B if any file from Module A imports any file from Module B.

Analyzing dependencies between modules can reveal a lot about the overall condition of a project. A project's architecture is considered valid when no two modules depend on each other cyclically. In other words, the dependency graph of all modules must form a directed acyclic graph (DAG).

Dependency Golden Rule

If Module A depends on Module B, then Module B must not depend on Module A.

This basic principle ensures a clear and maintainable structure, preventing tightly coupled modules and fostering scalability.