How useEffect is Different from useLayoutEffect in REACT JS.

React JS provides a number of built-in hooks that can significantly simplify our coding efforts, including?useState,?useEffect,?useRef,?useReducer,?useContext,?useMemo,?useCallback, and?useLayoutEffect.

While we may have a basic understanding of what each of these hooks does, in this article we will be delving into two of the most important hooks:?useEffect?and?useLayoutEffect. Specifically, we will explore the differences between these hooks and when to use each one for optimal performance and functionality in our React JS applications.

In order to fully grasp the?useEffect?and?useLayoutEffect?hooks in React JS, it's important to first understand the lifecycle of a React component.

There are three main phases a component goes through?Mounting,?Updating, and?Unmounting.

To better illustrate this concept, let's take a look at a simple class component that demonstrates the different lifecycle methods involved in each phase.

class Test extends React.Component {
  constructor(props){
    super(props)
    this.state ={
      isLoading : false,
    }
  }

  componentDidUpdate(prevProps , prevState) {
  // Some Code that will Run After Component Updates
  }
  
  componentWillUnmount() {
  // Some code that will run just Before Component unMounts
  }
  
  componentDidMount() {
   // Some code that will execute Right after Component Mounts 
  }
}        

The following code is an example of a simple functional component that demonstrates how life cycle methods in a class component can be replaced with a single hook?useEffect. By using this hook, we can simplify our code and avoid the complexity associated with class components.

const Test = () => 
  const [isLoading , setIsLoading] = useState(fasle);
  
  useEffect(() => {
    /* Some Code That Will Run After Component Mounts and After 
      Every Update Same Like componentDidMount and componentDidUpdate 
      with minor tweaks depends on dependency array */
    
    return () = > {
    /* This Block will run just Before Component unMounts same Like 
       componetWillUnMount and usually use for cleanup memory Leaks */
    }
  },[]) 
}{        

As we’ve discussed, the?useEffect?hook in React functional components is capable of replacing three of the life cycle methods that are typically used in class components. By utilizinguseEffectwe can streamline our code and reduce the overall complexity of our components.

It’s important to note that while the?useEffect?hook in React functional components is capable of replacing three life cycle methods typically used in class components, there is a subtle yet significant difference between the two. Understanding this difference is crucial to effectively utilize?useEffectin your components.

To enhance our comprehension of how these three life cycle methods are executed in class components, let’s take a look at a diagram that visually depicts their flow. This will provide us with a better understanding of how these methods work and how they differ from the?useEffect?hook.

The diagram shows that the first step of both functional and class components is the same, which is the Return. After this, the?componentDidMount?method is executed in the case of a class component, while the first function, which is the?useEffect, is executed in the case of a functional component. So far, everything seems to be in order. However, when an update occurs, the?componentDidUpdate?method in a class component is executed synchronously. This means that the code in this method must finish executing before the DOM can be updated.

In contrast, the code in the first function of the?useEffect?in a functional component runs asynchronously. This means that it does not block the DOM from updating before it finishes executing its code block. Therefore, if there is code that mutates the DOM in the?componentDidMount?and?componentDidUpdate?methods, we cannot use the?useEffect?in a functional component. This is because it creates a flickering issue, as the?useEffect’s?1st function does not block the return block (DOM updates) and runs while the update is happening, as well as after the 1st function finishes.

In a class component, the return block only runs (i.e., DOM updates) once, at the end of the?componentDidMount?lifecycle method. To replicate this same feature in a functional component, we need to use?useLayoutEffect?instead of useEffect. This is because?useLayoutEffect?is a synchronous method that executes after all DOM mutations are complete, just like the?componentDidUpdate?method in a class component. By using?useLayoutEffect, we can ensure that the DOM is updated only once, at the end of the lifecycle method.

Summary

The article explores the concepts of?useEffect?and?useLayoutEffect?by comparing them with the lifecycle methods of class components. It also discusses how to replicate the synchronous behavior of the?componentDidMount?method in class components in functional components. Additionally, it explains when to use useEffect versus?useLayoutEffect. Unlike?useEffect,?useLayoutEffect?is a synchronous method that blocks the DOM from updating or running the return block until it finishes executing.

If you found this article to be useful, kindly show your appreciation by giving it thumbs up.