Massive Components & How to Avoid Them

Why “massive components” are a problem

When a component grows into hundreds of lines, it usually starts mixing too many responsibilities:

• UI rendering
• state management
• data fetching
• business rules
• navigation / side effects
• formatting / mapping data to UI
• error handling
• sometimes even CRUD flows

What goes wrong:

1. Hard to read

   • You can’t hold the whole thing in your head.
   • New contributors get lost → slower progress.

2. Hard to change safely

   • One change can break unrelated parts.
   • Fear-driven development: “don’t touch it”.

3. Hard to reuse

   • Logic locked inside one place.
   • Copy-paste begins → bugs and bad practices multiply.

4. Hard to test

   • No clear boundaries.
   • You can’t easily test “just the rule” or “just this interaction”.
   • Tests become huge and brittle.

5. Harder code reviews

   • Reviewers spend time understanding structure instead of correctness.
   • Bugs hide in chaos.

What causes massive components

Common reasons:

• “I’ll just add one more feature here.”
• No mental model for splitting code.
• Fear that splitting = overengineering.
• Unclear separation between what the UI does vs what the business wants.
• Treating React file as “page script”.

React makes it easy to start small… and easy to grow messy if you don’t refactor early.

Separation of concerns (React edition)

Separation of concerns means each piece of code answers one kind of question.

In React, you usually want to separate:

1. UI / Presentation

   • “How does it look?”
   • Mostly JSX, small interactions.
   • Minimal logic.

2. Behavior / State

   • “How does it work?”
   • state transitions, handlers, UI rules.

3. Business logic

   • “What is allowed / what should happen?”
   • rules independent of UI.
   • can live in hooks, utility functions, services.

A clean component often feels like:

• JSX + wiring
• and “the thinking” is somewhere else.

Single Responsibility Principle (SRP)

SRP: “A unit should have one reason to change.”

In practice:

• If a component changes because of UI redesign, that’s one reason.
• If it changes because of business rules update, that’s a different reason.

If both reasons live in the same file → it will grow and become unstable.

Red flags that your component is “too big”

You don’t need a strict line limit. Look for signals:

Structure signals

• File is so long you scroll a lot.
• Many unrelated sections inside one component.
• Several independent blocks of state.

Logic signals

• Many nested in JSX.
• Complex derived values inline in render.
• Multiple early returns that are hard to follow.
• Long inline event handlers.
• The component effectively implements a workflow.

Responsibility signals

• It fetches data and formats/massages it and renders it and handles mutations.
• It contains rules like “admins can do X but only if Y…”
• It has both “page layout” and “input validation” and “API calls”.

Team signal

• You feel nervous to edit it.
• Reviewers say: “I don’t know what this does anymore.”

When to refactor (timing matters)

Refactor early, not when it’s on fire.

Good rule:

• If you needed mental effort to find where to add a feature, it’s time.
• If you’re about to add an exception or a new conditional, consider splitting first.
• If you copy-paste a logic block: stop and extract.

Refactoring is not a punishment, it’s maintenance.

What “good” looks like

A healthy React codebase usually has:

• Small components that do one thing.

• Custom hooks for reusable / encapsulated behavior.

• Helpers / pure functions for business rules.

• Explicit data flow

  • props down
  • events up

• Shallow JSX

  • most conditions are extracted into readable names.

You should be able to open a component and understand:

• what it renders
• what state it owns
• what it delegates elsewhere

in less than 1 minute.

Testability angle (why this matters)

If logic is trapped inside a huge component:

• tests must render the whole thing
• they depend on UI details
• small UI change breaks tests
• you can’t test rules independently

If logic is extracted:

• rules can be unit tested as pure functions
• hooks can be tested with small harnesses
• UI tests become simpler (“does it show x when y?”)

Smaller boundaries = cheaper tests.