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React Functional Components: Detailed Guide

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16th Apr, 2023
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React Functional Components: Detailed Guide

Introduction to React Functional Components

React components are the key ingredients of every react application. The ultimate goal of these components is to segregate the complete view into smaller segments. Each component helps to define the business logic and idea for that view. 

Simply put, there are mainly two types of React components. 

  • Class Components 
  • Functional Components

The following article will give you an in-depth idea of functional components React, their advantages, and the differences between react functional components and class components. 

Let’s get started!

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What Are Functional Components?

Functional components in React are JavaScript functions that are used to define reusable and modular UI components. They are the primary way of creating components in React and are also known as stateless components. One of the main reasons behind this is that they are simply responsible for rendering UI. This means their functionalities are only limited to accepting data and displaying the same in some form. 

Functional components in React can accept and use props, which are necessary for transferring information between components. Props are read-only, meaning the same props can return the same value, thus nullifying the need for React components to alter their values. Therefore, functional components are often referred to as React pure components.

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Advantages of Using Functional Components in React

The advantages of using functional components in React are many. The below-mentioned list highlights a few of them. 

  • Makes code easily readable – One of the biggest advantages of functional components is that it makes code easily readable and understandable by others. This is primarily because of two reasons. Firstly functional components do not modify any hidden state or have any hidden inputs. Secondly, the use of props helps readers to understand where things go and come from. 
  • Easy-To-Test – Functional components are also quite easy to test since they do not have any hidden states. Furthermore, every input generates only one output in functional components, which makes testing much easier. 
  • Makes Debugging Easier – Using props in functional components simplifies debugging by providing a predictable output. Unlike components with their own state, functional components with props eliminate the need for constant state checking. This streamlines the debugging process, making it more efficient.

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Differences Between Functional and Class 

Components in React

Here is a detailed guide to some of the key distinctions between React functional components and Class components.

Functional ComponentClass Component
A stateless component is a term often used to describe functional components. This is because they can only accept data and render the same in some form without using any logic. Class components are also commonly referred to as stateful components because they use logic and state.
React lifecycle methods, like componentDidMount, cannot be used in functional components. Multiple React lifecycle methods like componentDidMount, and componentWillUnmount can be used in class components.
Functional components do not make use of any constructors. Constructors are required in class components for the state to be stored.
They are easy to understand and involve fewer lines of code.Class components can be quite complex at times and require more lines of code. 

 

Creating Your First Functional Component in React

Below is a short and simple example of how you can create your first functional component in React

Let’s say you are trying to create a functional component called Car. The code for the same goes as follows.

function Car() {

     return <h2>Hi, I am a Car!</h2>;

}

Another important point to note here is that you can also create functional components with the help of the ES6 arrow function. 

Using Props in Functional Components

Props, also known as properties, facilitate data passing from one component to another. It can be extremely beneficial, especially when you want a dynamic data flow in your application. 

Typically there are two ways by which you can use props; one with the help of destructuring and the other without destructuring.

Here is a small example of how you can use props with destructuring. 

function Tool({username, favouriteTool}) {

  

    return (

      <div>

        <h1>My username is {username}.</h1>

        <p>My favourite design tool is {favouriteTool}.</p>

      </div>

    );

}

export default Tool

 

How you can use props without destructuring

 

function Tool(props) {

  const username = props.username;

  const favouriteTool = props.favouriteTool;

    return (

      <div>

        <h1>My username is {username}.</h1>

        <p>My favourite design tool is {favouriteTool}.</p>

      </div>

    );

}

export default Tool

 

Both approaches achieve the same result of accessing and using props within the component. Destructuring offers a more concise and readable code, especially when working with multiple props. On the other hand, directly accessing props from the props object is suitable for simpler scenarios.

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State Management in Functional Components

State management plays a vital role in building reliable user interfaces. React provides several hooks to facilitate state management, and one of the most commonly used hooks is ‘useState’. It takes the initial state value and generates an array containing two elements. 

The first element represents the current state value, and the second element is a function that allows you to update the state value. These two elements allow you to easily update the state according to user interactions and other events. 

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Lifecycle Methods in Functional Components

There are typically three phases in the whole lifecycle of React components. They are, namely, 

  • Mounting
  • Updating
  • Unmounting

Each phase consists of specific methods used to perform tasks at different stages. Traditionally, these methods were only available in class components. However, with the emergence of React hooks, you can also use these methods in functional components.

Wondering how? Let’s find out. 

 

useEffect Hook ()

 

The useEffect Hook () is a widely used React hook responsible for managing the side effects. It consists of two arguments: a dependency array and a callback function. 

 

useLayoutEffect () 

 

Similar to the useEffect hook, the useLayoutEffect is useful for measuring the size or position of a DOM element. The only difference is that useLayoutEffect runs synchronously after processing all the DOM mutations.

 

useCallback ()

 

The useCallback hook is a commonly used hook in functional components that is used to optimise the performance by memoising functions and preventing unnecessary re-renders of child components.

 

Hooks in Functional Components

React 16.8 introduced a new feature called Hooks, enabling you to use state or other React features without writing a class component. Here are a few examples of built-in hooks provided by React: 

 

useState ()

 

The useState () allows you to create or manage a state variable which can either be an object or a JavaScript primitive. For the latter, you can use const keywords to safeguard the state from direct mutation. Whereas, for the former, you can update the object’s properties easily and hassle-free. Here’s a small example:

 

const [isAuthenticated, setIsAuthenticated] = useState(false)

 

useContext ()

 

useContext () is beneficial, especially when accessing a state outside your component. With the help of the same, you can create a store within the app itself. Following this, you can select any part of the render component tree to scope it. In this manner, you can then utilise useContext () to expose the state and dispatch to the components.

 

useReducer ()

 

Modifying your state is crucial, especially when dealing with complex states. This is where useReducer () comes into play. It allows you to store state mutation logic safely inside a reducer instead of sprinkling it throughout the component or container. 

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Best Practices for Writing Functional Components in React

Contrary to other frameworks, React is unopinionated. This means it provides enough flexibility to write or structure your React code. Key points to remember while writing functional components in React:

  • Try using functional components and hook more often instead of class components.
  • Restrict the use of state only to situations when it is necessary.
  • Using the key as properties is important for efficiently rendering lists in React and help in updating and re-rendering components correctly.
  • To reduce the chances of errors, conduct tests for every component you create.
  • Opting for fragments is always advisable since <div> can potentially lead to poor user experience. 

Future of React Functional Components

Following their simple implementation, reusability and added assistance with hooks, React components have gained significant popularity among users, reflecting a promising future for the same. Hooks have provided more intuitive and concise ways to deal with side effects in functional components React, making them a fundamental part of React’s future updates as well. 

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As per the current implementation and assistance of functional components in React, the community actively anticipates enhanced features toward better developer productivity and performance. 

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Key Takeaways

With this, we come to an end of React functional components. Functional components have come a long way from a low-power building component to one of the key players in React application development. React’s flexibility and its benefits make it an excellent choice for building robust applications.

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Profile

Pavan Vadapalli

Blog Author
Director of Engineering @ upGrad. Motivated to leverage technology to solve problems. Seasoned leader for startups and fast moving orgs. Working on solving problems of scale and long term technology strategy.

Frequently Asked Questions (FAQs)

1What are the various types of React components?

React components can be divided into four categories. They are, namely, Functional components, React pure components, higher-order components, and class components.

2What is the function of Babel in React?

Babel is typically used to convert modern Javascript code into a version that can be run on any browser. Furthermore, it also enables developers to incorporate the latest JavaScript syntax into their components.

3What is the function of useEffect in React?

useEffect is primarily used in React to control any side effects that might arise in the components. These include gathering data and updating DOM and timers, among others.