📖 Part II: Modularity
Part 2: Modularity¶
“Modularity isn’t about folders. It’s about boundaries, ownership, and change without fear.”
In Part 2, we move from why structure matters to how modularity delivers clarity, flexibility, and velocity—especially in the early and mid-stages of software development.
Whether you're building an OCR-to-GPT receipt analyzer or a chatbot that extracts meaning from legal documents, the principle remains the same:
Organize by what changes together. Isolate what changes independently.
That’s modularity.
You don’t just want to build features—you want to build self-contained units of value, each with their own logic, tests, and UI.
This part teaches you how to design for that.
Why Modularity?¶
A modular folder structure helps you:
- Keep features isolated and independently testable
- Onboard new developers faster with clearer ownership
- Avoid cross-feature bugs and naming collisions
- Grow prototypes into real products without rewrites
It’s ideal for:
- Solo developers or small teams
- MVPs and internal tools
- Projects still shaping their domain boundaries
Modularity is not a shortcut—it's a strategy for maintainable independence.
What You'll Learn in Part 2¶
| Chapter | Key Idea |
|---|---|
| 7. Modular Architecture Overview | What modular structure means in practice, and when to choose it. |
| 8. Modular Folder Structure for React + Vite | Feature-first structure, folder anatomy, and keeping UI concerns scoped. |
| 9. Modular Folder Structure for FastAPI | Designing modular backends with clean services, routers, and schemas. |
| 10. Testing in Modular Projects | How to test per module, avoid global mock sprawl, and keep features testable in isolation. |
Modularity ≠ Simplicity¶
Modular apps often feel simpler because they reduce inter-feature dependency—but under the hood, they demand thoughtful composition.
This part doesn’t just show you the shape of a modular app.
It teaches you how to think modularly: which boundaries matter, how to organize logic per feature, and how to evolve structure as complexity grows.
By the end of Part 2, you’ll be able to:
- Structure both React and FastAPI projects using the feature-first philosophy
- Keep services, hooks, routes, and logic inside each feature
- Prevent shared-state bleed and keep testability high
- Prepare for the day when modular won’t be enough (spoiler: that’s Part 3)