Introduction: Why React Class Components Still Matter

While React Hooks and functional components dominate modern React development, class components are still widely used in:

• Legacy applications

• Enterprise projects

• Tutorials and older codebases

Understanding React Class Components is essential for:

• Maintaining existing code

• Working on team projects with mixed patterns

• Learning React’s core concepts like lifecycle methods and state handling

If you're serious about React, you must understand both functional and class components.

What Is a React Class Component?

A class component is an ES6 class that extends from React.Component. It must include a render() method and can manage state and lifecycle methods directly.

import React, { Component } from 'react';

class Welcome extends Component {
  render() {
    return <h1>Hello, {this.props.name}</h1>;
  }
}

Structure of a Class Component

✅ Basic Syntax

class MyComponent extends React.Component {
  constructor(props) {
    super(props);
    // Initialize state
    this.state = {
      count: 0
    };
  }

  // Class method
  increment = () => {
    this.setState({ count: this.state.count + 1 });
  };

  render() {
    return (
      <div>
        <p>Count: {this.state.count}</p>
        <button onClick={this.increment}>Increment</button>
      </div>
    );
  }
}

⚙️ Key Concepts in Class Components

1. State Management

Use this.state to define and access component state.

this.state = { isVisible: true };         // Initialization
this.setState({ isVisible: false });      // Updating state

2. Props Handling

Access props with this.props.

render() {
  return <h1>Welcome, {this.props.username}</h1>;
}

3. Lifecycle Methods

Functional vs Class Component Comparison

Complete Working Example

// File: App.js
import React, { Component } from 'react';

class Counter extends Component {
  constructor(props) {
    super(props);
    this.state = {
      count: 0
    };
  }

  increment = () => {
    this.setState((prevState) => ({
      count: prevState.count + 1
    }));
  };

  componentDidMount() {
    console.log("Component mounted!");
  }

  componentDidUpdate() {
    console.log("Component updated!");
  }

  componentWillUnmount() {
    console.log("Component will unmount!");
  }

  render() {
    return (
      <div style={{ padding: '1rem', textAlign: 'center' }}>
        <h2>React Class Counter</h2>
        <p>Count: {this.state.count}</p>
        <button onClick={this.increment}>Add</button>
      </div>
    );
  }
}

export default Counter;

Tips & Common Pitfalls

✅ Best Practices

• Always call super(props) in the constructor.

• Use arrow functions for methods to preserve this.

• Group lifecycle logic in respective methods (componentDidMount, etc.).

• Prefer functional components for new projects, but learn class components for legacy support.

❌ Common Mistakes

• ❌ Forgetting this. when accessing state or props.

• ❌ Not binding class methods (if not using arrow functions).

• ❌ Calling setState in render()—causes infinite loop.

• ❌ Mutating state directly (this.state.count++) instead of using setState.

Class vs Functional Component Syntax Summary

Conclusion: Why You Should Still Learn React Class Components

Even though React Hooks are the present and future, class components remain relevant in:

• Enterprise-grade applications

• Older codebases

• Complex integrations

Knowing how to write and read class components makes you a well-rounded React developer capable of working on any project.

Pro Tip: Learn class components to understand the evolution of React and debug legacy code like a pro.

Key Takeaways

• React Class Components use ES6 classes and support internal state and lifecycle methods.

• Still widely used in legacy and enterprise codebases.

• Understanding class components improves your ability to maintain and refactor existing projects.

• Use arrow functions or bind methods to correctly reference this.