DEV Community

Petr Janik
Petr Janik

Posted on • Edited on

Classes vs Functional components in React

#react #javascript

In React, we can either use classes or functions for our components.

Classes

As you may have noticed in the first part of this series, we can create a React component as a class. To do so, we have to extend a React.Component class and implement its render() method.
This method must return either one root element or a fragment.

  • This class renders a <div> and its contents. 
export default class TodoList extends React.Component {
  render() {
    return (
      <div>
        <h1>Todo list</h1>
      </div>
    );
  }
}
Enter fullscreen mode Exit fullscreen mode
  • This class renders a fragment. 
export default class TodoList extends React.Component {
  render() {
    return (
      <>
        <h1>Todo list</h1>
        <h1>Second element</h1>
      </>
    );
  }
}
Enter fullscreen mode Exit fullscreen mode

Alternatively

export default class TodoList extends React.Component {
  render() {
    return (
      <React.Fragment>
        <h1>Todo list</h1>
        <h1>Second element</h1>
      </React.Fragment>
    );
  }
}
Enter fullscreen mode Exit fullscreen mode

Using fragments enables us to have multiple elements on the same level without having any <div> around them.

Functions

Instead of classes, we can write our components as functions.
The rules for the export and import are the same as with classes.
The function itself must return either one root element or a fragment.

Default export

  • Named function 
export default function TodoList() {
  return (
    <div>
      <h1>Todo list</h1>
    </div>
  );
}
Enter fullscreen mode Exit fullscreen mode
  • Anonymous function

When using default export, we may omit the name completely.
However, I do not recommend this.

export default function () {
  return (
    <div>
      <h1>Todo list</h1>
    </div>
  );
}
Enter fullscreen mode Exit fullscreen mode
  • Named arrow function 
const TodoList = () => {
  return (
    <div>
      <h1>Todo list</h1>
    </div>
  );
};

export default TodoList;
Enter fullscreen mode Exit fullscreen mode
  • Anonymous arrow function 
export default () => {
  return (
    <div>
      <h1>Todo list</h1>
    </div>
  );
};
Enter fullscreen mode Exit fullscreen mode

Named export

  • Named function 
export function TodoList() {
  return (
    <div>
      <h1>Todo list</h1>
    </div>
  );
}
Enter fullscreen mode Exit fullscreen mode
  • Named arrow function 
export const TodoList = () => {
  return (
    <div>
      <h1>Todo list</h1>
    </div>
  );
};
Enter fullscreen mode Exit fullscreen mode

Another not so fashionable option could be

export const TodoList = function () {
  return (
    <div>
      <h1>Todo list</h1>
    </div>
  );
};
Enter fullscreen mode Exit fullscreen mode

Personally, I prefer writing the React components as arrow functions.

Top comments (2)

Collapse
 
asher_dev profile image
Asher •

There is one caveat, however. Using default export of the arrow function is only possible after the declaration.

You could just export default anonymous arrow function



export default () => {
  return ( <h1>Hello World</h1> )
}
Enter fullscreen mode Exit fullscreen mode
Collapse
 
petr7555 profile image
Petr Janik •

Thank you, I have corrected it.

Read next

jacksonsantin profile image

Login/cadastro com firebase + Vue JS #PASSO 1️⃣

Jackson Dhanyel Santin -

peboycodes profile image

Stop Making These Component Mistakes

Paul Adeyele -

geraldhamiltonwicks profile image

5 Essential Software Metrics for Quality Assurance

Gerald Hamilton Wicks -

laustke profile image

I created a video tutorial on how to make a responsive sidebar using CSS and vanilla Javascript

Louis Austke -