When you're early in React development, you focus on making things work. Later, as projects grow, you realize that architecture and design principles are even more important than syntax.

That's where the SOLID Principles come in — to help you build scalable, flexible, and maintainable React applications.

What is SOLID?

SOLID is an acronym for 5 software design principles that help developers:

Write better-structured code
Reduce complexity
Avoid code rot and technical debt
Make systems easier to understand, extend, and test

These principles were popularized by Robert Martin aka Uncle Bob and are especially powerful when working on large apps or team projects, including modern React.js applications.

Let's dive deep into what SOLID really means for React, with real-world examples and extra professional insights.

Definition: A class, module, or component should have only one reason to change — it should only have one responsibility.

In simpler terms: Each component, hook, function, or module should do ONE thing and do it well.

Why It Matters:

Separation of concerns: Easier to understand what each piece of the system does.
Easier maintenance: When a bug occurs, you know exactly where to look.
Better reusability: Components and hooks become more generic and reusable.
Simpler testing: Single-responsibility units are easier to mock and test.

Without SRP:

Components become bloated ("God Components").
Minor changes risk breaking unrelated features.

Common SRP Violation in React:

A component that handles data fetching, state management, and UI rendering simultaneously.

Example of Bad SRP:

function UserProfile({ userId }) {
  const [user, setUser] = useState(null);

  useEffect(() => {
    fetch(`
/api/user/$
{userId}
`
)
      .then((res) => res.json())
      .then((data) => setUser(data));

  }, [userId]);

  return (
    
      {user?.name}
      {user?.bio}
    
  );

}

Problem: Fetching logic + display logic = mixed responsibilities.

Applying SRP Correctly:

Break it into two:

Hook for fetching user data.
Component for displaying.

function useUser(userId) {
  const [user, setUser] = useState(null);

  useEffect(() => {
    fetch(`
/api/user/$
{userId}
`
)
      .then((res) => res.json())
      .then((data) => setUser(data));

  }, [userId]);

  return user;

}

function UserProfile({ userId }) {
  const user = useUser(userId);

  if (!user) return Loading...;

  return (
    
      {user.name}
      {user.bio}
    
  );

}

useUser → Data fetching
UserProfile → UI

Best Practice Tip:

Try to keep your components under 50 lines. If they grow bigger, extract responsibilities.

Open/Closed Principle (OCP)

Definition: A module, class, or component should be open for extension but closed for modification.

Meaning: You should be able to add new functionality without altering existing code.

Why It Matters:

Future-proofing: You can evolve systems by adding new features without touching stable, tested code.
Reduces bugs: Modifying old code always carries risk.
Enables safe scaling: New requirements don't destroy your architecture.
Cleaner team collaboration: Developers can extend behavior safely without fighting over old files.

Without OCP:

Adding features feels like playing Jenga — every change risks a collapse.

Common OCP Violation:

Hardcoding new behavior into old components.

Bad Example:

function Notification({ type, message }) {
  if (type === "success") return {message};

  if (type === "error") return {message};

  if (type === "info") return {message};

}

Problem: Every time a new type comes (warning, alert), we have to edit this component.

Applying OCP Correctly:

Use a mapping or configuration-based approach.

const notificationStyles = {
  success: "success",
  error: "error",
  info: "info",
};

function Notification({ type, message }) {
  const className = notificationStyles[type] || "default";

  return {message};

}

To add new types, just update notificationStyles.
No core code change needed.

Best Practice Tip:

Favor composition and configurations over conditionals whenever possible.

Liskov Substitution Principle (LSP)

Definition: If a component, function, or class is a subtype, it should be replaceable for its parent type without breaking the program.

In other words, If you extend something, you should be able to use it anywhere the original thing was used, without surprises.

Why It Matters:

Predictable behavior: Child components/hooks don't cause unexpected bugs.
Encourages abstraction: Forces you to design general, flexible contracts.
Boosts composability: New features are easier to plug in.
Helps unit testing: Substitutes (mocks/stubs) can easily replace real services.

Without LSP:

Extending systems causes fragile bugs that are hard to detect.

Common LSP Violation:

Components that expect specific implementations, not abstractions.

Bad Example:

function PaymentProcessor({ payment }) {
  if (payment.type === "paypal") {
    return ;

  }
  if (payment.type === "stripe") {
    return ;

  }
}

Problem: Tight coupling to specific services.

Applying LSP Correctly:

Pass components or handlers dynamically.

function PaymentProcessor({ PaymentComponent }) {
  return ;

}

// Usage

Now, any payment method can be passed without changing PaymentProcessor.

Best Practice Tip:

Prefer dependency injection over hardcoding "what to render".

Interface Segregation Principle (ISP)

Definition: Clients should not be forced to depend on methods they do not use.

Meaning: Make small, specific interfaces/components instead of large, bloated ones.

Why It Matters:

Simplifies usage: Components receive only what they need.
Easier maintenance: Changes in one part don't break unrelated users.
Improves readability: Developers instantly understand a component's API.
Enables flexibility: Specialized components for different situations.

Without ISP:

Developers are forced to provide unnecessary props, causing confusion.

Common ISP Violation:

Huge components are expecting too many props.

Bad Example:

function DataTable({ data, onSort, onFilter, onExport, onPaginate }) {
  // Basic table that might not even need export or pagination
}

Problem: Most consumers may not need all these actions.

Applying ISP Correctly:

Split the components:

function BasicTable({ data }) {
  return (
    
      {/* Basic table rendering */}
    
  );

}

function AdvancedTable({ data, onSort, onFilter, onExport, onPaginate }) {
  return (
    
      {/* Advanced table rendering */}
    
  );

}

Basic consumers stay simple.
Advanced consumers opt into complexity.

Best Practice Tip:

Make separate versions or HOCs/hooks to extend features, rather than making everything "fat."

Dependency Inversion Principle (DIP)

High-level modules should not depend on low-level modules. Both should depend on abstractions.

Definition: High-level modules should not depend on low-level modules. Both should depend on abstractions.

Meaning: Your core business logic should not directly depend on technical details.

Why It Matters:

Testability: You can mock external services easily.
Decoupling: Changes in API layers or databases don't ripple into UI layers.
Flexibility: Easily swap APIs, services, storage methods.
Cleaner architecture: Business logic stays business logic.

Without DIP:

Changing an API requires rewriting your UI.

Common DIP Violation:

UI components directly calling APIs.

Bad Example:

function ProductsList() {
  const [products, setProducts] = useState([]);

  useEffect(() => {
    fetch("https://www.syedalinaqihasni.com/api/products")
      .then((res) => res.json())
      .then((data) => setProducts(data));

  }, []);

  return products.map((p) => {p.name});

}

Problem: tightly coupled to API details.

Applying DIP Correctly:

Abstract fetching logic:

function useProducts(service) {
  const [products, setProducts] = useState([]);

  useEffect(() => {
    service.fetchProducts().then(setProducts);

  }, [service]);

  return products;

}

// Service layer
const productService = {
  fetchProducts: () => fetch("https://www.syedalinaqihasni.com/api/products").then((res) => res.json()),
};

// Component
function ProductsList() {
  const products = useProducts(productService);

  return products.map((p) => {p.name});

}

Want to test with mock products? Inject a mock service.

Best Practice Tip:

Introduce a service layer and inject it into components, rather than embedding network calls inside your UI.

Final Thoughts

SOLID is not a strict rulebook. It's a mindset.

When you apply SOLID in React:

SOLID teaches you how to structure code for long-term success — not just "quick working prototypes."
In React, it leads to smaller components, better hooks, easier testing, and more scalable apps.
Mastering SOLID is the difference between "I can build apps" and "I can build systems."

It's what separates “hacky apps” from “professional-grade systems.”

Quick Question:

Which SOLID principle do you think most React developers ignore the most? (I'll reply with examples!)

#ReactJS #SOLIDPrinciples #FrontendEngineering #SoftwareArchitecture #CleanCode #ReactBestPractices

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