What is class component and Functional component?

Table of Contents

1. Introduction to React Components
2. Class Components
3. Syntax and Structure
4. State and Lifecycle Methods
5. When to Use Class Components
6. Functional Components
7. Syntax and Structure
8. Props and State
9. Hooks
10. When to Use Functional Components
11. Class vs Functional Components: A Comparison
12. Syntax
13. State Management
14. Lifecycle Methods
15. Performance
16. Readability and Maintainability
17. Frequently Asked Questions (FAQ)
18. Conclusion

Introduction to React Components

React components are self-contained pieces of code that represent a part of the user interface. They can be reused throughout your application, making your code more modular and easier to maintain. Components in React can be defined using either classes or functions.

Class Components

Syntax and Structure

Class components are defined using ES6 classes and extend the React.Component base class. They must include a render() method that returns the JSX to be rendered. Here’s an example of a class component:

import React from 'react';

class MyComponent extends React.Component {
  render() {
    return <div>Hello, {this.props.name}!</div>;
  }
}

export default MyComponent;

State and Lifecycle Methods

Class components have their own state and can use lifecycle methods. State is an object that represents the internal data of a component and can be modified using the setState() method. Lifecycle methods are special methods that allow you to hook into different phases of a component’s life, such as when it mounts, updates, or unmounts.

Some commonly used lifecycle methods include:

• componentDidMount(): Called after the component is mounted to the DOM.
• componentDidUpdate(): Called after the component updates.
• componentWillUnmount(): Called before the component is unmounted from the DOM.

Here’s an example of a class component with state and lifecycle methods:

import React from 'react';

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

  componentDidMount() {
    console.log('Component mounted');
  }

  componentDidUpdate(prevProps, prevState) {
    console.log('Component updated');
  }

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

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

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

export default Counter;

When to Use Class Components

Class components are a good choice when you need to:

• Manage state within the component.
• Use lifecycle methods to perform actions at specific points in the component’s life.
• Handle user interactions and events.
• Integrate with older codebases that heavily rely on class components.

Functional Components

Syntax and Structure

Functional components are defined as JavaScript functions that accept props as an argument and return JSX. They are simpler and more concise compared to class components. Here’s an example of a functional component:

import React from 'react';

const MyComponent = (props) => {
  return <div>Hello, {props.name}!</div>;
};

export default MyComponent;

Props and State

Functional components receive props as an argument, which are read-only and cannot be modified directly. However, with the introduction of hooks in React 16.8, functional components can now have state and lifecycle-like behavior.

Hooks

Hooks are functions that allow you to add state and other React features to functional components. The most commonly used hooks are:

• useState: Allows you to add state to functional components.
• useEffect: Allows you to perform side effects, such as fetching data or subscribing to events.
• useContext: Allows you to consume context values in functional components.

Here’s an example of a functional component using hooks:

import React, { useState, useEffect } from 'react';

const Counter = () => {
  const [count, setCount] = useState(0);

  useEffect(() => {
    console.log('Component mounted or updated');
    return () => {
      console.log('Component will unmount');
    };
  }, []);

  const increment = () => {
    setCount((prevCount) => prevCount + 1);
  };

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

export default Counter;

When to Use Functional Components

Functional components are a good choice when you:

• Have simple, stateless components that only receive props and render UI.
• Want to use hooks to add state and lifecycle-like behavior to your components.
• Prefer a more concise and readable syntax.
• Are building new applications or components from scratch.

Class vs Functional Components: A Comparison

Frequently Asked Questions (FAQ)

1. Q: Can I use state in functional components?
   A: Yes, with the introduction of hooks in React 16.8, functional components can now have state using the useState hook.

2. Q: Are class components deprecated in React?
   A: No, class components are still supported in React and are not deprecated. However, the React team encourages the use of functional components with hooks for new development.

3. Q: Can I use hooks in class components?
   A: No, hooks are only available in functional components. If you need to use hooks, you’ll need to convert your class component to a functional component.

4. Q: When should I choose class components over functional components?
   A: If you need to manage state, use lifecycle methods, or integrate with older codebases that heavily rely on class components, you should choose class components. Otherwise, functional components with hooks are generally recommended for new development.

5. Q: Can I mix class and functional components in the same application?
   A: Yes, you can use both class and functional components in the same React application. They can coexist and interact with each other seamlessly.

Conclusion

In this article, we explored the differences between class components and functional components in React. Class components are defined using ES6 classes and provide state management and lifecycle methods. Functional components, on the other hand, are simpler and more concise, defined as JavaScript functions. With the introduction of hooks, functional components can now have state and lifecycle-like behavior.

When deciding between class and functional components, consider factors such as state management needs, lifecycle methods, performance, and readability. In general, functional components with hooks are recommended for new development, while class components are still useful in certain scenarios.

Ultimately, both class and functional components have their strengths and use cases. Understanding the differences between them will help you make informed decisions when building your React applications.