CODEWITHSUNDEEP
reactjs
Justin
Justin

Reputation: 1479

function App() vs class App extends Component in the App.js file

I'm following a tutorial on React (https://www.youtube.com/watch?v=sBws8MSXN7A - dated January 3, 2019) and created a React app with npx create-react-app *app_name*. The App.js file this command generated on my computer is different from what this command generated for the person giving the tutorial. Has React changed since then or is it possible I downloaded something wrong?

My App.js:

import React from 'react';
import logo from './logo.svg';
import './App.css';

    function App() {
      return (
        <div className="App">
          <header className="App-header">
            <img src={logo} className="App-logo" alt="logo" />
            <p>
              Edit <code>src/App.js</code> and save to reload.
            </p>
            <a
              className="App-link"
              href="https://reactjs.org"
              target="_blank"
              rel="noopener noreferrer"
            >
              Learn React
            </a>
          </header>
        </div>
      );
    }

export default App;

Tutorial's App.js:

import React, { Component } from 'react'; //different
import logo from './logo.svg';
import './App.css';

    class App extends Component { //different
      render() ( //different
        // The rest of the file is the same
        <div className="App"> 
          <header className="App-header">
            <img src={logo} className="App-logo" alt="logo" />
            <p>
              Edit <code>src/App.js</code> and save to reload.
            </p>
            <a
              className="App-link"
              href="https://reactjs.org"
              target="_blank"
              rel="noopener noreferrer"
            >
              Learn React
            </a>
          </header>
        </div>
      );
    }

    export default App;

Upvotes: 43

Views: 32954

Answers (4)

Ilya Kushlianski
Ilya Kushlianski

Reputation: 968

There are basically two ways of writing components in React: functional and class components. The given examples are no different except for this aspect.

React has recently updated their documentation website and switched all examples from class components to function components. You can check it out https://react.dev/learn

Upvotes: 19

Omar Saade
Omar Saade

Reputation: 591

The obvious differences are in the syntax and hints are derived from their names in how they will be written. They both render JSX (which is React’s way of writing HTML and JavaScript), however for the class component you define a class that extends the React.Component library. Additionally, the class component utilizes a render() method. Here’s an example:

App.js: functional component

import React, { Component } from 'react';
import './App.css';

function App() {
    return (
        <h1>hello</h1>
    );
}

export default App;

App.js: class component

import React, { Component } from 'react';

class App extends Component {
    render() {
        return (
            <h1>hello</h1>
        );
    }
}

export default App;

Upvotes: 2

A . L. I
A . L. I

Reputation: 341

There is one major difference between these methods of defining a component. It's related to the state of the particular React component.

So, Function-Based Components => Are also called Stateless components reason being they don't update to any changes that are being applied to a particular component.

So, If I want to change some value in this <p>Hi, Welcome</p> on a button press to <p>Welcome Back</p> It wouldn't be possible to use function-based components.

On the other hand, Class-Based Components => Are also called Stateful Components, being that they update to changes that occur to the component.

So, the previous example would work.

Personally, I would say a simple way to remember is Functional Components for static data and Class-Based Components for dynamic and interactive data.

Upvotes: 12

WMRamadan
WMRamadan

Reputation: 1210

The most obvious difference is the syntax. A functional component is just a plain JavaScript function which accepts props as an argument and returns a React element.

A class component requires you to extend from React.Component and create a render function which returns a React element. This requires more code but will also give you some benefits.

A functional component doesn’t have its own state. If you need a state in your component you will either need to create a class component or you lift the state up to the parent component and pass it down the functional component via props.

Another feature which you cannot use in functional components are lifecycle hooks. The reason is the same as for state, all lifecycle hooks are coming from the React.Component which you extend from in class components. So if you need lifecycle hooks you should probably use a class component.

Conversely, functional components allowed to use hooks where class components are not allowed to.

Upvotes: 21

Related Questions