From Spaghetti to Scalable: How I Modularized a Growing Frontend Codebase

Introduction: The "Oh No" Moment

At some point in my career, I took over a large React app that seemed fine at first — until it wasn't. 😅

The project had evolved over time, but instead of growing gracefully, it became an unmanageable beast:

❌ A custom state manager — hard to debug & scale.
❌ Massive UI components — mixing business logic, API calls, and UI.
❌ Multiple UI versions for different clients — but all versions lived in the same codebase.
❌ Releases were painful — changing one part could break something completely unrelated.

At some point, I realized: This is unsustainable.

👉 This is the story of how I refactored that messy frontend into a modular, scalable, and maintainable system without breaking everything along the way.

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🎯 TL;DR

• Messy frontend code? Modularization is the key!

• Break down your code into components, features, and domains.

• Keep UI, logic, and data handling separate.

• NX monorepos solve interdependency issues.

• Start small, refactor in steps, and enforce structure with tools.

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Phase 1: The Giant Monolithic App Era

At the start, our React app was an all-in-one monolith:

• Custom state management. We had built our own instead of using Redux or anything else (Context API was not that powerful yet).

• UI + logic bundled together. a single component could be over 500 lines long.

• Multiple UI versions in one repo. Each client required a slightly different UI, but instead of separating them, all versions coexisted in the same codebase.

• A single repo handled everything. State, API calls, business logic, and UI, making it hard to maintain and even harder to onboard new developers.

Biggest Pain Points:

🚨 Scaling was impossible. As we added more clients, the complexity multiplied.
🚨 Code duplication was everywhere. Reusing functionality meant lots of copy-pasting.
🚨 UI modifications were a nightmare because each client had different design needs, we had tons of if statements handling different layouts.

Lesson Learned:

A single repository containing everything isn't just inefficient — it's a ticking time bomb.

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Phase 2: Splitting the Monolith — The First Step to Modularization

Realizing the mess, I decided to refactor the app into separate repositories, each handling a specific concern.

The New Modular Structure:

✅ A React component library 📦

• Contained state, API interactions, and core functionality.

• Single source of truth for all logic — no more duplication.

✅ A separate UI module 🎨

• A pure extension of Bootstrap CSS — no JavaScript, just styling.

• Clients could now have different layouts without affecting the app logic.

✅ A React app for pages & UX 🏗️

• Handled routing, layouts, and page composition.

• Different apps could now be built using the same API + component library.

What Changed?

🚀 More flexibility — we could create apps with different layouts without duplicating code.
🚀 Easier maintenance — frontend developers could work on UI without touching business logic.
🚀 Cleaner separation of concerns — each module had a clear responsibility.

👉 The refactor was a game-changer. But it introduced a new challenge: managing interdependent packages.

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Phase 3: The NPM Link Hell & How NX Saved the Day

After splitting the project into multiple repos, we ran into another problem:

⚠️ Local development became painful. We relied on npm linking to work across multiple co-dependent packages.
⚠️ Syncing changes was slow. Any update to one package had to be manually managed in others.
⚠️ Onboarding became complicated. New developers had to manually set up multiple repos just to get started.

I realized that managing separate repos was becoming its own problem.

The Solution: NX Monorepo

To simplify development, we moved all modules into an NX workspace:

✅ Unified repository structure — All projects lived in one place.
✅ Built-in dependency graph — NX automatically understood how modules were connected.
✅ Faster builds — NX only rebuilt the parts of the code that changed.

👉 The migration strategy was key. To avoid disruption, we:

1. Created the app from scratch in the NX workspace.
2. Copied the existing React component library without changing logic, just refactored class components into hooks.
3. Introduced two additional modules to improve the architecture and add features.

What Changed?

🚀 Modular, scalable development — each team could now work on their own package without affecting others.
🚀 Faster iteration — no more npm linking headaches!
🚀 Better collaboration — dedicated teams worked on separate parts of the frontend.

👉 With NX, we finally had a system that was both modular and manageable.

Next Steps: Refining the NX Architecture 🚀

While migrating to an NX monorepo significantly improved our workflow, there's still room for further modularization. The next phase will focus on enhancing maintainability and scalability by:

✅ Breaking Down Features into Micro Packages
Currently, our React component library contains both core functionality and feature-specific logic. To better align with NX's best practices, we'll:

• Extract feature-specific modules into standalone NX packages (e.g., @myorg/task-list, @myorg/profile).
• Ensure each feature package is independent and reusable across multiple applications.
• Reduce interdependencies between features to simplify development and deployment.

✅ Introducing Documentation with NX Storybook
To improve*developer experience and collaboration, we'll:

• Integrate NX Storybook for our UI components and feature modules.
• Provide interactive documentation where developers can preview and test components.
• Standardize our design system and API contracts to maintain consistency across projects.

With these improvements, our NX workspace will become even more scalable, well-documented, and developer-friendly — allowing teams to work more efficiently with clearly defined boundaries between features.

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Final Takeaways: Lessons I Learned the Hard Way 😅

1️⃣ Start modularizing early. Don't wait until the project is too big to handle.
2️⃣ Separate UI, logic, and state from the beginning. This saves countless hours of refactoring later.
3️⃣ Avoid unnecessary complexity. Modularization should make things easier, not harder.
4️⃣ Consider a monorepo for interdependent projects. NX solved many problems for us.
5️⃣ Migrating gracefully is key. Doing it step by step prevented downtime.

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Conclusion: Keep It Simple, Keep It Scalable 🚀

Modularization isn't about making things complex — it's about making them manageable.

💡 If I were to start a frontend project today, I would:

✅ Use a component-based architecture from day one.
✅ Decouple UI from business logic immediately.
✅ Consider a monorepo for interconnected projects.
✅ Ensure teams have ownership over separate modules.

🔹 Have you ever had to refactor a messy frontend codebase?
🔹 What's your go-to strategy for keeping your projects modular?

💬 Drop a comment — I'd love to hear your experiences!

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📌 Want to Learn More?

🔗 Stay tuned for my next article on Micro-Frontends: When and When Not to Use Them!

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Comments

[Peter Vivo]

Absolute right!