Can you use useEffect in class component? useEffect equivalent for class components

Front-end technology has come a long way in the last decade. Developing a front-end web application is no longer as straightforward as it once was. Nowadays, there are several front-end frameworks and libraries accessible. We will learn about the corresponding useEffect equivalent class component methods we may use in place of the useEffect Hook.

One such library is React.js. Facebook published it in 2013. Even though it is a library, we commonly refer to it as a framework. React is concerned only with the display layer of an application. React is the View (V) in the MVC architectural paradigm. We can write JS right in our HTML since we build the views in JSX (JavaScript XML).

Before React 16.8, class components were the sole mechanism to monitor a React component’s state and lifecycle. People viewed functional components as second-class citizens. They couldn’t manage state, logic, or many other React capabilities, and we only used them to display extremely minimal UI components.

React 16.8 addressed these issues by providing React Hooks, which allowed developers to access specific react capabilities in functional components.

This post will go through the useEffect Hook. It is the most crucial Hook in React.js for managing the component’s lifecycle.

What are Hooks?

Hooks are a new addition to React.js version 16.8. They let you leverage React library features like lifecycle methods, state, and the context in functional components without converting them into class-based components. Class components include many boilerplate codes, whereas hooks have shorter components and are easier to comprehend.

Hooks also address the issue of code repetition among components. We utilize Hooks inside function components instead of classes. It does not mean React is abandoning classes, but hooks are an effective alternative.

Hooks allow you to divide a component into separate functions. Instead of splitting code into Lifecycle methods, we may structure and segregate your code into smaller functional components.

There are a few rules which we must follow while using React Hooks.

We can call Hooks at the top level of a component: We cannot use Hooks within loops, conditions, or nested functions.
We can only invoke Hooks by another React Hook or a React Functional Component: We may only call Hooks by another React Hook or a React Functional Component; any other JavaScript function cannot call them.

What is the useEffect Hook?

The useEffect Hook allows you to implement side effects in function components. Side effects can occur in addition to a component’s core processes, such as external API interactions, state variable modification, and data retrieval. Functional components could not perform these side effects before React introduced this hook.

It accepts two arguments: a callback function and a dependency array. The dependency array holds a list of component scope values like props, context, and state variables. It instructs the Hook to run if its value changes. React will execute the Hook after each render if we don’t provide any arguments.

useEffect(() => {
  // run side-effects
}, [...])Code language: JavaScript (javascript)

Can we use the useEffect equivalent Hook in a class component?

We’ve previously seen that React added hooks for React Functional Components, and we can only use them within a React Functional Component or another Hook. As a result, we cannot utilize any React Hook (including useEffect) within a class-based component.

We have “Life Cycle Methods” for class-based components that we may utilize to monitor the component’s lifecycle and take appropriate actions. We may use these lifecycle methods instead of Hooks when working with class-based components.

React component lifecycle

Lifecycles are the different states that a React component goes through. The lifecycle of a React component consists of three parts: Mount, Update, and Unmount.

Mount

Mounting a component involves adding or mounting the relevant node to the DOM.

Update

During the update phase, the React component gets updated following the mounting process. Without changes, the component would stay in the DOM as we had constructed it initially. We must change many components, either by changing the state or props. As a result, they must also go through the updating process.

Unmount

The final process is unmounting. The component gets deleted from the DOM at this point.

Hook useEffect for class component

Let’s look at the useEffect equivalent for class-based components now. We’ll look at how we may accomplish similar behavior to useEffect by utilizing the lifecycle methods of class-based components.

Mount

As previously stated, mounting a component involves adding or mounting the required node to the DOM. If we want to run some function on the component mount, we write the following code using the useEffect Hook.

useEffect(() => {
  // run side-effects
}, [])Code language: JavaScript (javascript)

Because we only want to invoke the callback supplied to the useEffect equivalent once when the component mounts, the dependency array is empty.

We will use the componentDidMount lifecycle method to achieve a similar behavior while using a class-based component. This method gets invoked whenever the component is mounted. To use this method, we will write the following code.

componentDidMount() {
  // do something
}Code language: JavaScript (javascript)

Update

As mentioned earlier, the React component updates following the mounting process during the update phase. If we want to run some function when the component updates, we write the following code using the useEffect Hook.

useEffect(() => {
  // run side-effects
}, [dependency1, dependency2])Code language: JavaScript (javascript)

The callback function will run whenever variables in the dependency array change.

We will use the componentDidUpdate lifecycle method to achieve a similar behavior while using a class-based component. In addition, it takes previous props as arguments. This method gets invoked whenever the component is updated. To use this method, we will write the following code.

componentDidUpdate(prevProps) {
  // do something
}Code language: JavaScript (javascript)

Unmount

As mentioned earlier, the React component gets deleted from the DOM during the unmounting phase. If we want to run some function when the component unmounts, we write the following code using the useEffect equivalent Hook.

useEffect(() => {
  // run side-effects

  return () => {
    // run cleanups
  }
}, [])Code language: JavaScript (javascript)

You’ll notice we’re returning another function from our callback function here. We term this function as a “Cleanup” function. It is triggered whenever the component is unmounted. We’ve also given an empty dependency array since we want our callback method to run only when the component is mounted. It is not required; we may also utilize variables within the dependency array.

We will use the componentWillUnmount lifecycle method to achieve a similar behavior while using a class-based component. This method gets invoked whenever the component is unmounted. To use this method, we will write the following code.

componentWillUnmount() {
  // do something
}Code language: JavaScript (javascript)

Conclusion

In this post, we examined React Hooks and why they are essential. We also looked at the useEffect equivalent, one of the most critical hooks in React.js for managing the component’s lifecycle. We also analyzed the React component’s lifecycle. Finally, we learned about the appropriate class component methods we may use in place of the useEffect Hook.

Thank you so much for reading ?