React Components Functional Vs Class Components Complete Guide

Top 10 Questions and Answers: React Components – Functional vs. Class Components

Answer: Functional components are simple JavaScript functions that return a React element and can be expressed as pure functions or arrow functions. They were initially stateless but gained the ability to manage state with React Hooks introduced in version 16.8.

Class components, on the other hand, require you to extend React.Component and include a render method that returns a React element. They are used when you need to use lifecycle methods or maintain state before the introduction of hooks.

2. Can Functional Components have State in React?

Answer: Yes, functional components can now manage their own state using the useState hook along with other state management hooks like useReducer. For example:

import React, { useState } from 'react';

function Counter() {
    const [count, setCount] = useState(0);
    
    return (
        <div>
            <p>You clicked {count} times</p>
            <button onClick={() => setCount(count + 1)}>
                Click me
            </button>
        </div>
    );
}

3. Which component type should I use for managing side effects in React?

Answer: Side effects like data fetching, subscriptions, or manually changing the DOM are managed using the useEffect hook in functional components, which is equivalent to componentDidMount, componentDidUpdate, and componentWillUnmount lifecycle methods in class components.

Example:

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

function ExampleComponent(){
  const [data, setData] = useState([]);

  useEffect(() => {
    // Fetching data from an API
    fetch('https://api.example.com/data')
      .then(response => response.json())
      .then(data => setData(data));

    // Cleanup function
    return () => {
       // Code to clean up after component unmounts
    }
  }, []);

  return (
    <>
      {data.map(item => <div key={item.id}>{item.name}</div>)}
    </>
  )
}

4. Do Functional Components offer better performance than Class Components?

Answer: Generally, functional components with hooks are more optimized by React internally. Hooks help in reducing unnecessary re-renders through the use of useState, useEffect and others, which make the code more efficient and performant.

However, the actual difference might not be noticeable unless you're working on a large scale application with many nested components. React's reconciler has been optimized significantly for functional components with hooks.

5. Can I use Class Components with modern React features?

Answer: While most modern React features focus on functional components and hooks, it is still possible to use class components. Some lifecycle methods like componentDidMount and componentWillUnmount are only available in class components, though their functionalities can often be replicated using hooks in functional components. Also, features based on context API, such as static contextType and contextTypes, are more straightforward in class components.

6. How do you handle Context within Class and Functional Components?

Answer:

In functional components:

• Using useContext hook, which allows you to subscribe to context changes.

import React, { useContext } from 'react';
import MyContext from './MyContext';

function FunctionalComponent(){
  const value = useContext(MyContext);
  return (
    <div>{value}</div>
  )
}

In class components:

• Use this.context inside your class to access the context (you’d need to specify static contextType).
• Alternatively, use the <Context.Consumer> pattern which accepts a function as a child that receives the current context value.
• Or you can also use higher-order component (HOC) pattern context.Consumer() to pass down the context value.

class ClassComponent extends React.Component {
    static contextType = MyContext;
  
    render(){
      const value = this.context;
      return <div>{value}</div>;
    }
}

// Consumer pattern
<MyContext.Consumer>
  {value => <div>{value}</div>}
</MyContext.Consumer>

// HOC pattern
withContext(MyContext)(({ value }) => <div>{value}</div>);

7. Can Class Components use Hooks?

Answer: No, class components cannot use React hooks directly as they are designed specifically to work with functional components. If you need hooks' functionalities in a class component, you can refactor it to a functional component or use other patterns like HOCs or render props.

8. What are the advantages of using Functional Components over Class Components?

Answer: Functional components offer several advantages:

• Simpler syntax: They can often be written with less boilerplate code.
• State management via Hooks: You can use the useState and useReducer hooks to manage state within functional components.
• Lifecycle methods via Hooks: The useEffect hook allows you to manage lifecycle methods, which simplifies the code structure.
• Less confusion about the binding of this: There are no issues regarding the need to bind this to class methods, making the code cleaner and easier to understand.
• Improved performance: In some cases, functional components may result in fewer renders due to optimizations in React's reconciliation process.
• Composition instead of inheritance: Functional components encourage the use of composition through higher-order components (HOCs), render props, and custom hooks, which makes for more modular and reusable code.

9. Why would you prefer Class Components if you're still writing them?

Answer: While the shift towards functional components and hooks is predominant, here are some scenarios where class components could still be preferable:

• Legacy codebases that have not yet refactored to use hooks.
• Specific use cases requiring older lifecycle methods or features more naturally supported in class components, such as the usage of contextType or certain third-party libraries designed for older React versions.
• If you're using decorators (though decorators support in class components is experimental).

10. How do you decide whether to use a Functional Component or a Class Component?

Answer: Given the improvements and increased readability brought by functional components and hooks, most new codebases use functional components. However, when deciding which component type to use, consider the following factors:

• State Management: If your component doesn’t need state or side effects, you should go with a functional component. If it does, decide if you prefer hooks or class lifecycles.
• Codebase Consistency: In maintaining a consistent style across your project, check what pattern the majority of components use. Refactoring existing class components to functional is usually straightforward.
• Learning Curve: New developers to React might find it easier to understand state management and side effects with hooks in functional components than class-specific lifecycle methods.
• Third-Party Library Compatibility: Some third-party libraries might still be optimized toward a specific pattern - this could influence whether you use class or functional components.