Understanding Functional Components Vs. Class Components in React

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Overview

There are two approaches to writing a React component in the realm of React. One employs a class, while the other employs a function. Moreover, functional components have recently grown in popularity. So the question arises about the difference between these two types of components.

Introduction

Developers must write more than a thousand lines of code that follow the conventional DOM structure when creating a single-page application. If any modifications are required that make updating difficult, a component-based method is proposed to address this problem. This approach separates the entire application into logical code groups called components.

React Component is compared to a wall's brick. It dramatically simplifies UI creation. The components that are used ultimately determine the UI, and they all combine into a parent component.

What are Functional Components?

In react, the easiest way to define a component is using the functional component.

Function components are a means to create components in React that do not have their state and only return JSX. They are JavaScript functions that might or might not include parameters that contain data. We can write a function that accepts the props(properties) argument and outputs the displayed result. The example below demonstrates a functional component that is valid.

React hooks are used by functional components to provide the same functionality as class components.

Since the functional component does not store or handle the state, it is also referred to as a stateless component. React does, however, provide a hook called useState() that enables function components to keep track of their state.

There is no life cycle for a functional component. For the functional component to access the component’s various stages, React offers a hook called useEffect().

We employ a functional component when we are sure that our component does not need to connect with or work with any other component. In other words, these components do not need information from other components. However, we can group several functional components under a single functional component.

Function components need substantially less code to write than class components and are simpler to understand.

What are Class Components?

In comparison to functional components, class components are more complex. To develop class-based components in React, we can use JavaScript ES6 classes. To define a React component class, you need to extend React.Component. You must develop a render method that returns a React element by extending from React.Component. Data can be passed between classes and between class components. A valid class component is displayed in the example below.

Due to their ability to contain or manage local states, class components are also known as stateful components.

The life cycle of a class component is accessible through specific callback APIs, which also provide access to each life cycle event.

Your application will be inefficient if class-based components are used when they are not necessary.

Rendering JSX

Let us see the difference in rendering in-class components vs functional components.

Functional components are plain JavaScript functions, and they return JSX. Following is the syntax

You can also look at the example below without the arrow function if you are unfamiliar with the arrow functions that were added in ES6.

On the other side, you must create a class that extends React.Component when establishing a class for a component. The render method will return the JSX to be rendered.

An identical example is shown here without the use of destructuring.

Passing Props

props, that is properties, are passed into the React component. Additionally, it is used for transferring data between components.

It can be tricky to comprehend passing props, so let us look at how they are expressed in both class and functional components.

Say we have props with the name "Scaler Topics" for our example.

While using class components, we use this.props to access the name props.

When working with functional components, we use the syntax props.name to send the props as an argument to our function, and we need not worry about the this keyword, and the syntax becomes cleaner and more understandable.

Handling State

The state object, which is a built-in component of React, is used to manage component actions. Re-rendering of the component will occur whenever the state object changes.

And we are all aware that dealing with state variables is inevitable when working on a React project. Up until recently, handling state was only possible in class components, but with the introduction of React Hook useState in version 16.8, developers can now create stateful functional components. Here, we will create a basic counter that counts up from 0 and increments by 1. With each click of the button, we will see the class component vs functional component comparison.

Handling state in Functional Components

UseStateHook, which accepts an argument of the initial state, is required to use state variables in a functional component. In this instance, the starting state of the count will be 0, as we start with 0 clicks.

Of course, you may use any type that JavaScript supports, including null, strings, and even objects, as your starting state. We are destructuring the array in the manner shown on the left because useState returns the current state as well as a function that updates it. If you are uncertain about the two array elements, think of them as a state and its setter. To make the connection between the two variables clear, we gave them the names count and setCount in this example.

Handling State in Class Components

Although a class component manages the state somewhat differently, the concept remains the same. We must first understand the significance of the React.Component Constructor. It is defined in the official documentation as follows:

“The constructor for a React component is called before it is mounted. When implementing the constructor for a React.Component subclass, you should call super(props) before any other statement. Otherwise, this.props will be undefined in the constructor, which can lead to bugs.”

All the state variables you are trying to utilize will be undefined if the constructor is not implemented and super(props) is not called. So let us start by defining the function constructor. You will create a state object with a state key and initial value inside the constructor. Additionally, within JSX, we retrieve the value of the state key we set in the constructor to display the count by using this.state.count. The setter is essentially the same; the syntax is different.

A different option is to create an onClick function. Recall that the setState function accepts one or more arguments of type state, along with optional props.

Functional Components vs Class Components

Now let us highlight and see the Class components vs Functional components differences.

Functional ComponentsClass Components
The simplest definition of a functional component is a simple JavaScript pure function that takes an argument called props and returns a React element (JSX).You must build a render function that returns a React element when creating a render function for a class component by extending from React.Component.
Functional components do not use any render methods.The render() method returning JSX is required (which is syntactically similar to HTML).
When a function is returned, it can no longer be maintained because functional components work from top to bottom.Different life cycle methods are kept alive, performed, and triggered based on the phase of the class component after it is created.
Also referred to as stateless components because they merely accept data and render it in some way, they are mostly in charge of rendering user interfaces.Because they use logic and state, they are also known as stateful components.
Functional components cannot use React lifecycle methods, such as componentDidMount.Class components can use React lifecycle methods (for example, componentDidMount, componentWillUnmount etc).
To make functional components stateful, hooks can be used with ease. Example:
const [name,SetName]= 
React.useState(‘ ‘)
Hook implementation inside a class component requires a different syntax. Example:
constructor(props)
{
super(props);
this.state = {name: ‘ ‘}
}
There is no use of constructors.Since the state needs to be stored, constructors are utilized.
Functional components are more efficientClass components are a little inefficient
Functional components require fewer lines of code and are easy to understandClass components are complex and require more lines of code.

Which Component Should You Use?

Class components have been replaced by functional components in React version 16.8. The code is clearer and less complex because functional components are more condensed. They do not contain inherited members or lifecycle methods, which might or might not be necessary for code functionality.

Functional components can be used for anything that can be achieved with class components. The sole exception is that React offers a unique class component called Error Boundaries that is exclusive to the class component and cannot be copied as a function component.

Class components have state and lifecycle methods attached to them since they extend from React.Component. Your ability to manage state as a result of their presence depends on your ability to predict when lifecycle events will happen and how to react to them. Classes also need further setup to perform API calls for data or for the component, which is often implemented via the constructor. Without using design patterns, it is more challenging to share logic across several class objects, which makes the code more complex and challenging to maintain.

It is also important to note that the React team is supporting more functional components that can replace or even outperform class components with React hooks. In addition, the React team previously stated that they would reduce the number of checks and memory allocations in functional components to improve efficiency.

The use of class components supports inheritance design patterns, whereas the use of functional components promotes composition. Currently, the composition is regarded as a best practice in programming, which is why functional components rather than class components are used the majority of the time in new React code. Nevertheless, React continues to support class components for legacy purposes.

Although both methods have advantages and disadvantages, it can be said that functional components will soon overtake modern React, which means functional components are better in class component vs functional component comparison.

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Conclusion

In this Class components vs functional component comparison, we have covered the following points.

  • The only way to change the lifecycle and add states to components was through class components. It has changed since the introduction of hooks, which provided functional components with the same opportunities as classes did.
  • There is a major difference in the syntax, which is observed in the declaration of components, passing props, handling state etc.
  • Functional components need fewer lines of code than class components.
  • Class components make use of the this keyword which creates lots of confusion and makes it harder to understand the code and the functional component has resolved this issue by eliminating the use of the this keyword.
  • Functional components are better to use than class components, and it can be observed by the fact that the React team is promoting the use of functional components over class components.
  • Though the React team has been promoting the use of functional components, the class components are not going to be deprecated shortly because it has been used extensively by the developers.