When to use a Class Component over a Function Component in ReactJS?

ReactJS provides two main ways to create components: Class Components and Function Components. With the introduction of React Hooks in version 16.8, Function Components became more powerful and are now commonly preferred. However, there are still scenarios where Class Components might be a better choice or necessary.

What Are Class Components?

Class Components are ES6 classes that extend the React.Component base class. They allow you to use lifecycle methods and manage state without additional libraries or hooks.

//App.js

import React, { Component } from 'react';

class App extends Component {
    constructor(props) {
        super(props);
        this.state = {
            message: 'Welcome to React!'
        };
    }
    changeMessage = () => {
        this.setState({ message: 'Thanks for visiting!' });
    };
    render() {
        return (
            <div>
                <h1>{this.state.message}</h1>
                <button onClick={this.changeMessage}>Change Message</button>
            </div>
        );
    }
}
export default App;

Output

What Are Function Components?

Function Components are simpler JavaScript functions that take props as an argument and return JSX. With React Hooks, they can now manage state and side effects.

import React, { useState } from 'react';

function App() {
    const [message, setMessage] = useState('Welcome to React!');
    return (
        <div>
            <h1>{message}</h1>
            <button onClick={() => 
                setMessage('Thanks for visiting!')}>Change Message</button>
        </div>
    );
}
export default App;

It will give the same output as give by class component.

Difference Between Class and Function Components

When to Use Class Components?

Although Function Components are now more popular, Class Components may still be relevant in the following cases:

• Legacy Codebases: In older React projects, you might encounter Class Components extensively. When making updates or maintaining these projects, it’s easier to stick with the existing pattern rather than refactoring everything to Function Components.
• Strict Lifecycle Control: If your component relies heavily on lifecycle methods like shouldComponentUpdate, componentDidCatch, or getDerivedStateFromProps, Class Components are a natural fit since these methods are not available in Function Components.
• Complex State Logic: While useReducer can handle complex state logic in Function Components, Class Components provide a built-in way to manage such logic without introducing additional hooks.
• Third-Party Libraries Without Hook Support: Some older libraries or tools are built with the assumption that you’re using Class Components. Integrating these libraries might require Class Components.
• Error Boundaries: As of now, Error Boundaries can only be implemented using Class Components. Error Boundaries are used to catch JavaScript errors in a component tree and display fallback UI.

When to Use Function Components?

Function Components are preferred in most modern React applications for their simplicity and flexibility. Use them when:

• Building New Projects: Start with Function Components to use React’s latest features.
• Using Hooks: They allow powerful features like useState, useEffect, and custom hooks.
• Performance Optimization: Function Components are typically more lightweight and easier to optimize.
• Readability and Maintenance: The concise syntax makes them easier to understand and maintain.

Conclusion

Class Components are becoming less common with the rise of Hooks, but they still have valid use cases in legacy systems, complex lifecycle management, and specific scenarios like Error Boundaries. For most new React applications, Function Components are the recommended choice due to their simplicity, modern features, and better performance.