When to use ES6 class based React components vs. functional ES6 React components?

Question

After spending some time learning React I understand the difference between the two main paradigms of creating components.

My question is when should I use which one and why? What are the benefits/tradeoffs of one over the other?

---

ES6 classes:

import React, { Component } from 'react';

export class MyComponent extends Component {
  render() {
    return (
      <div></div>
    );
  }
}

---

Functional:

const MyComponent = (props) => {
    return (
      <div></div>
    );
}

I’m thinking functional whenever there is no state to be manipulated by that component, but is that it?

I’m guessing if I use any life cycle methods, it might be best to go with a class based component.

Solution 1

New Answer: Much of the below was true, until the introduction of React Hooks.

• componentDidUpdate can be replicated with useEffect(fn), where fn is the function to run upon rerendering.

• componentDidMount methods can be replicated with useEffect(fn, []), where fn is the function to run upon rerendering, and [] is an array of objects for which the component will rerender, if and only if at least one has changed value since the previous render. As there are none, useEffect() runs once, on first mount.

• state can be replicated with useState(), whose return value can be destructured to a reference of the state and a function that can set the state (i.e., const [state, setState] = useState(initState)). An example might explain this more clearly:

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

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

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

default export Counter

As a small aside, I have heard a number of people discussing not using functional components for the performance reasons, specifically that

"Event handling functions are redefined per render in functional components"

Whilst true, please consider if your components are really rendering at such a speed or volume that this would be worth concern.

If they are, you can prevent redefining functions using useCallback and useMemo hooks. However, bear in mind that this may make your code (microscopically) worse in performance.

But honestly, I have never heard of redefining functions being a bottleneck in React apps. Premature optimisations are the root of all evil - worry about this when it's a problem.

---

Old Answer: You have the right idea. Go with functional if your component doesn't do much more than take in some props and render. You can think of these as pure functions because they will always render and behave the same, given the same props. Also, they don't care about lifecycle methods or have their own internal state.

Because they're lightweight, writing these simple components as functional components is pretty standard.

If your components need more functionality, like keeping state, use classes instead.

More info: https://facebook.github.io/react/docs/reusable-components.html#es6-classes

Solution 2

UPDATE March 2019

Building on what was stated in my original answer:

Are there any fundamental differences between React functions and classes at all? Of course, there are — in the mental model.

https://overreacted.io/how-are-function-components-different-from-classes/

UPDATE Feb 2019:

With the introduction of React hooks, it seems as though the React teams wants us to use functional components whenever possible (which better follows JavaScript's functional nature).

Their motivation:

1.) It’s hard to reuse stateful logic between components
2.) Complex components become hard to understand
3.) Classes confuse both people and machines

A functional component with hooks can do almost everything a class component can do, without any of the draw backs mentions above.

I recommend using them as soon as you are able.

Original Answer

Functional components aren't any more lightweight than class based components, "they perform exactly as classes." - https://github.com/facebook/react/issues/5677#issuecomment-241190513

The above link is a little dated, but React 16.7.0's documentation says that functional and class components:

are equivalent from React’s point of view

https://reactjs.org/docs/components-and-props.html#stateless-functions

There is essentially no difference between a functional component and a class component that just implements the render method, other than the syntax.

In the future (quoting the above link):

we [React] might add such optimizations

If you're trying to boost performance by eliminating unnecessary renders, both approaches provide support. memo for functional components and PureComponent for classes.

-https://reactjs.org/docs/react-api.html#reactmemo

-https://reactjs.org/docs/react-api.html#reactpurecomponent

It's really up to you. If you want less boilerplate, go functional. If you love functional programming and don't like classes, go functional. If you want consistency between all components in your codebase, go with classes. If you're tired of refactoring from functional to class based components when you need something like state, go with classes.

Solution 3

Always try to use stateless functions (functional components) whenever possible. There are scenarios where you'll need to use a regular React class:

• The component needs to maintain state
• The component is re-rendering too much and you need to control that via shouldComponentUpdate
• You need a container component

UPDATE

There's now a React class called PureComponent that you can extend (instead of Component) which implements its own shouldComponentUpdate that takes care of shallow props comparison for you. Read more

Solution 4

As of React 17 the term Stateless Functional components is misleading and should be avoided (React.SFC deprecated, Dan Abramov on React.SFC), they can have a state, they can have hooks (that act as the lifecycle methods) as well, they more or less overlap with class components

Class based components

• state
• lifecycle methods
• memoization with React.PureComponent

Functional components:

• state (useState, useReducer hooks)
• lifecycle methods (via the useEffect, useLayoutEffect hooks)
• memoization via the memo HOC

Why i prefer Funtional components

• React provide the useEffect hook which is a very clear and concise way to combine the componentDidMount, componentDidUpdate and componentWillUnmount lifecycle methods
• With hooks you can extract logic that can be easily shared across components and testable
• less confusion about the scoping

React motivation on why using hooks (i.e. functional components).

View more solutions

Comments

[Rotareti]

Always try to use stateless functions (functional components) whenever possible. I have read ten people say that. Still none of them gave an explanation why.

[Diogo Cardoso]

In an ideal world, most of your components would be stateless functions because in the future we’ll also be able to make performance optimizations specific to these components by avoiding unnecessary checks and memory allocations. This is the recommended pattern, when possible. More info: facebook.github.io/react/docs/…

[door_number_three]

@rotareti I don't know if you feel you got your question answered, but pure functions are much simpler to understand, test and maintain. Given the same parameters, they always render the same thing. Components that maintain state and change when lifecycle events occur are harder to understand. Not to say they aren't sometimes needed, but I hope it's clear that if their advantages are not needed, all they do is add unwanted boilerplate and overhead with no benefits.

[Dobes Vandermeer]

You will also want to create a Component class if you have your own event handler definitions. That way you can pre-bind those event handlers to the component in the constructor instead of creating a fresh new function on every render. Note this is not needed if all your event handlers come from props.

[Dennis]

What about functionality that isn't keeping state, but is tightly coupled to the component, e.g. determine some dynamic attribute for the render.

[Arian Acosta]

This is the best article about the difference between the two types of components in React: code.tutsplus.com/tutorials/…

[jeffski13]

I think making every component extend React.Component makes the code more readable, especially for the new people. It is nice when you see a component created the same way every time. Like @Galupuf said, simple components just have one method called "render()". It is also nice to make everything extend React.Component because when you want to start binding "this", having state, etc. you don't have to refactor everything, you can just add what you need.

[Greg]

As of React 16.8, you can use state in a functional component, via the useState hook.

[polkovnikov.ph]

As of React 16.8, you can do almost everything in functional components, and all the effects can finally be modularized with only a minimal impact on performance.

[johannchopin]

Where have you find the info where Facebook officially recommends using functional components wherever possible?

[n00b]

I'm also curious about the Facebook officially recommends using functional components wherever possible.

[Garrett]

Seems FB's recommendation has changed over time: In 2016-June, they recommended functional components, in 2016-Oct they recommended functional components when you don't need state, ES6 classes when you do and in 2016-Nov, their recommendation was removed altogether.

[Garrett]

Note that the quoted Facebook recommendation is no longer existent (see my comment above).

[General Grievance]

What do you mean by, "Classes can't be reused?"

[Danilo Souza Morães]

points 2 and 3 are as redundant as they are unfounded.

[Danilo Souza Morães]

classes are one big component that cant be broken down or reused? What if you break a component into multiple class components?

[EresDev]

We break down classes all the time. All design patterns are about breaking down classes.

[CodeConnoisseur]

@jeffski13 so you are in favor of Class based react components? Or functional components?

[coder9833idls]

Fair enough, making smaller classes in a sense is the same thing. You can have a small class component and nest it in different places. I meant a parent class component can't be re-used if you wanted to only render one element in it in different places. You can call an element inside a functional component in different places and not render the entire component- they are simply a function. You can call an element inside a function in a library without calling the entire function. If it is a class component, you can't do something like import fooFn.barElement, you have to call the entire class.

[OzzyTheGiant]

@rotareti, I can see the benefit of functional components (memoization), but from my personal encounters and experiences, I think functional components are much HARDER to reason about. I think people think all functional components will be written with just a few lines of code but many times I have found MASSIVE functional components doing way too many things at once; functions and event handlers everywhere; code is unreadable! Such code should be written in an object oriented way: either the component needs to be class-based or all those handlers need to be written as a class service.

[Joe C.]

In your "new answer", could you answer when to use function vs class? Or are you saying that with hooks, functions are always preferred over class?