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A Guide to using useEffect Hook for React Lifecycle Methods

Aakash Rao
~ 10 min read | Published on May 09, 2024





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React Hooks which were first introduced in React version 16.8 has brought a significant change to the way developers write code in React. They offer a neat and effective approach to reusing stateful behavior across components.

One of the most widely used Hooks in React is the useEffect Hook, which enables developers to manage side effects in functional components, simulating the functionality of the lifecycle methods available in class components.

The React Component Lifecycle defines the different stages that a component goes through, from the time it is mounted on the screen to the time it is removed. Understanding the React Component Lifecycle is critical to writing high-quality React applications.

In this comprehensive blog, we will try to dive deep into the concept of using the useEffect Hook to apply React's Lifecycle Methods in functional components.

We will explore the importance of using useEffect Hook for Lifecycle Methods and how it can make a developer's life easier while using it with functional components. We will learn how to implement it with various examples of Lifecycle methods, including mounting, updating, and unmounting.

So without waiting further let’s dive in…

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Overview of Lifecycle Methods with React Component Lifecycle

React is a powerful and popular JavaScript library used for building user interfaces. React's Lifecycle methods were a key feature that set it apart from other frameworks in the past, allowing developers to manage the behavior of components during different stages of their lifecycle.

While the introduction of hooks has made React more approachable and reduced the need for lifecycle methods in many cases, there are still situations where they are useful, such as when working with class components or integrating with external libraries that rely on them.

Therefore, It’s important to understand how React works and the Lifecycle methods, which made it easy to control the different phases of a component's life, such as when it is generated, modified, or destroyed. 

By leveraging these methods, developers can create more efficient and robust applications, manage state and props effectively, and optimize their components for performance.

Image showing the React Lifecycle stages and different methods

As displayed in the image, React Component Lifecycle refers to the various stages that a component experiences from the point at which it is created until it is removed from the DOM. The component lifetime comprises three main stages: Mounting, Updating, and Unmounting.

Let’s explore each of these stages and their methods with some examples.

Mounting phase:

The lifecycle of a React component starts with the mounting phase. It occurs when the component is first added to the DOM. The component is initialized, and its state and props are set, during this stage.

The purpose of the mounting phase is to set up the component's initialization and any required infrastructure, such as event listeners or API queries. By the end of the mounting phase, the component is fully set up and ready to be interacted with.

During the mounting phase, the component's state and props are set and the initial DOM structure is generated. Now that we understand the mounting, let's explore the componentDidMount() lifecycle method that is used during the mounting phase in greater detail.

Mounting phase with componentDidMount() method

The componentDidMount() is the lifecycle method that is invoked immediately following the mounting of a React component in the DOM, during the mounting phase of the component's lifecycle.

The purpose of this method is to give the component the freedom to perform any setup that may be required, such as setting up event listeners, obtaining data from an API, or communicating with other third-party libraries. Let’s try to take a glimpse of the use case with greater detail.

Fetching Data from an API:

Getting information from an API is one of the most frequent uses of componentDidMount(). A component might need to fetch data to display on the page when it is first mounted. This method can be used to make the API call and set the component's state with the data that is returned.
Quick example:

class ZipyComponent extends React.Component {
  constructor(props) {
    super(props);
    this.state = {
      data: null,
      isLoading: true,
      error: null,
    };
  }

  async componentDidMount() {
    try {
      const response = await fetch("https://example.com/api/data");
      if (!response.ok) {
        throw new Error("Failed to fetch data");
      }
      const data = await response.json();
      this.setState({ data, isLoading: false });
    } catch (error) {
      this.setState({ error: error.message, isLoading: false });
    }
  }

  render() {
    const { data, isLoading, error } = this.state;

    if (isLoading) {
      return <div>Loading...</div>;
    }

    if (error) {
      return <div>Error: {error}</div>;
    }

    return (
      <div>
        <h1>Data from API</h1>
        <ul>
          {data.map((item) => (
            <li key={item.id}>{item.name}</li>
          ))}
        </ul>
      </div>
    );
  }
}

In this code example we are using the componentDidMount() to fetch data from an API and update the component's state.

The componentDidMount() makes a GET request to an API endpoint using the fetch() method. If the response is successful, the data is parsed as JSON and set as the component's state. If there is an error, the error message is set in the component's state. 

There might be some cases where it might be a problem with debugging errors, especially when fetching data from such APIs. To overcome this you can use Zipy which is an intelligent debugging and error-monitoring tool designed for ReactJS applications. 

With Zipy you can easily monitor your component's state and quickly identify and resolve errors in your code. It provides detailed stack traces that help you pinpoint errors and resolve them quickly.

Updating phase:

The Updating phase is the second phase in the React component lifecycle. This phase begins when the component's state or props change and the component need to be re-rendered.

During this updating phase, React updates the DOM to reflect the changes in the component's state and/or props. The purpose of the Updating phase is to ensure that the component's presentation reflects its current state and props. 

By updating the DOM as necessary, React ensures that the component's UI remains responsive and up-to-date. It also allows components to optimize performance by preventing unnecessary re-renders, which can improve the overall performance of the application.

Let’s explore the lifecycle methods that are used during the updating phase in greater detail.

Updating phase with shouldComponentUpdate() & componentDidUpdate() method

We have two specific methods that can be used with this specific lifecycle of the component, such as the shouldComponentUpdate() and componentDidUpdate().

The shouldComponentUpdate() is a lifecycle method in React that allows a component to decide whether or not it should update based on the changes in props or state. 

By default, React re-renders the component every time props or state change. However, if the updated props or state have no effect on the component's UI or output, re-rendering can be prevented by returning false in shouldComponentUpdate().
Quick Example:

class ZipyComponent extends React.Component {
  constructor(props) {
    super(props);
    this.state = {
      count: 0,
    };
  }
  shouldComponentUpdate(nextProps, nextState) {
    // Only re-render if the count has changed
    if (nextState.count !== this.state.count) {
      return true;
    }
    return false;
  }
  handleClick = () => {
    this.setState({ count: this.state.count + 1 });
  };
  render() {
    return (
      <div>
        <h1>Count: {this.state.count}</h1>
        <button onClick={this.handleClick}>Increment</button>
      </div>
    );
  }
}

In the shouldComponentUpdate() method, we're checking if the updated state.count is different from the previous this.state.count. If it is, we're returning true, which allows the component to re-render. If it's not, we're returning false, which prevents the component from re-rendering.

As a result, when the user clicks the button, only the <h1> element displaying the count value will update, rather than the entire component. This optimization can lead to improved performance and a better user experience.

Another lifecycle method, which can be used during the updating phase is the componentDidUpdate() method which is called after a component updates and re-renders in the DOM. It is useful for performing additional actions after the component has been updated, such as updating a third-party library or making additional API calls.

The method receives two arguments: prevProps and prevState, which represent the component's previous props and state, respectively. These can be compared to the current props and state to determine what changed and how to update the component accordingly. Let’s understand its use with an example.
Quick example:

class ZipyComponent extends React.Component {
  constructor(props) {
    super(props);
    this.myChart = null;
  }
  componentDidMount() {
    // Initialize the chart library on component mount
    this.myChart = new Chart(this.canvasRef.current, {
      type: "bar",
      data: {
        labels: ["Red", "Blue", "Yellow", "Green", "Purple", "Orange"],
        datasets: [
          {
            label: "# of Votes",
            data: [12, 19, 3, 5, 2, 3],
            backgroundColor: [
              "rgba(255, 99, 132, 0.2)",
              "rgba(54, 162, 235, 0.2)",
              "rgba(255, 206, 86, 0.2)",
              "rgba(75, 192, 192, 0.2)",
              "rgba(153, 102, 255, 0.2)",
              "rgba(255, 159, 64, 0.2)",
            ],
            borderColor: [
              "rgba(255, 99, 132, 1)",
              "rgba(54, 162, 235, 1)",
              "rgba(255, 206, 86, 1)",
              "rgba(75, 192, 192, 1)",
              "rgba(153, 102, 255, 1)",
              "rgba(255, 159, 64, 1)",
            ],
            borderWidth: 1,
          },
        ],
      },
      options: {
        scales: {
          yAxes: [
            {
              ticks: {
                beginAtZero: true,
              },
            },
          ],
        },
      },
    });
  }

  componentDidUpdate(prevProps, prevState) {
    // Update the chart data if the component's data changes
    if (this.props.data !== prevProps.data) {
      this.myChart.data.datasets[0].data = this.props.data;
      this.myChart.update();
    }
  }
  render() {
    return (
      <div>
        <canvas ref={this.canvasRef} />
      </div>
    );
  }
}

In this example, the ZipyComponent component sets up a chart library when it first loads, using componentDidMount(). Each time the component receives an update, the componentDidUpdate() method is activated. This method checks whether the data prop of the component has changed since the last update. If there's been a change, it updates and redraws the chart using the update() method from the library.

The main reason for using componentDidUpdate() is to allow the component to take extra steps after it updates and redraws. This lifecycle method provided by React lets components manage their behavior precisely, leading to applications that are more effective and perform better. Now that we understand the phases of mounting and unmounting, let's move on to the final phase, which is the Unmounting phase.

Unmounting phase:

The unmounting phase in React takes place when a component is removed from the DOM. This occurs when the component is no longer necessary, the user moves to a new page, or when the application is shut down.

The purpose of this phase is to clear out resources that aren't needed anymore, like event listeners or timers. If these aren't cleaned up properly, they can cause memory leaks and reduce the application's performance.

During this phase, React provides a method called componentWillUnmount(). This method allows developers to eliminate any resources associated with the component before it is removed from the DOM. Let’s delve into how componentWillUnmount() is implemented in real scenarios

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Unmounting phase with componentWillUnmount() method

The componentWillUnmount() method is a lifecycle method in React that is called just before a component is removed from the DOM. 

This method allows developers to perform any necessary cleanup tasks before the component is unmounted. The purpose of this method is to release any resources that were allocated during the mounting or updating phase of the component's lifecycle. 

This could include removing event listeners, canceling timers or network requests, or releasing any other resources that the component may have created. Let’s understand this with a simple example.

class ZipyComponent extends React.Component {
  constructor(props) {
    super(props);
    this.state = {
      count: 0,
    };
    this.intervalId = null;
  }
  componentDidMount() {
    this.intervalId = setInterval(() => {
      this.setState((prevState) => ({ count: prevState.count + 1 }));
    }, 1000);
  }
  componentWillUnmount() {
    clearInterval(this.intervalId);
  }
  render() {
    return (
      <div>
        <p>Count: {this.state.count}</p>
      </div>
    );
  }
}

In this example, the componentDidMount() method sets up an interval to update the component's state every second. In the componentWillUnmount() method, the interval is cleared using the clearInterval() method to prevent any memory leaks or unnecessary resource usage after the component is removed from the DOM.

Overall, the componentWillUnmount() method is useful for cleaning up any resources that were created during the component's lifecycle. This ensures that the application remains performant and avoids any memory leaks or unnecessary resource usage. 

Now that we know  how each of these methods works, you can create a small version and deploy your React app by applying these methods to fully understand their implementation.

As React has evolved, certain lifecycle methods have been marked as deprecated, signaling that they are not supported in the latest versions and might be removed in future updates. Let's look at these deprecated methods and understand the recommended alternatives.

Deprecated Methods Overview

1. componentWillMount():
Previously used for setting up tasks before a component mounted in the DOM, componentWillMount() was often triggered multiple times due to updates, leading to performance drawbacks. In React 16.3, this method was phased out and replaced with getDerivedStateFromProps() for updating state before rendering, and componentDidMount() for tasks after the component mounts.

2. componentWillReceiveProps():
This method was once used to update the state in response to prop changes. However, it led to unnecessary re-renders and potential misuse. With React 16.3, it's been succeeded by getDerivedStateFromProps() to handle prop changes more smoothly, and componentDidUpdate() for post-update actions.

3. componentWillUpdate():
Called before updates to props or state, componentWillUpdate() could lead to performance issues by being invoked too frequently. It was replaced in React 16.3 by getSnapshotBeforeUpdate() to capture DOM state before changes, and componentDidUpdate() to work after updates.

4. getSnapshotBeforeUpdate():
Introduced as a replacement for componentWillUpdate(), this method allows capturing information from the DOM just before it is potentially altered by an update. It's part of the modern lifecycle methods and provides a safe way to handle DOM information pre-update.

Moving Forward with Modern Methods

These deprecated methods are considered legacy and should be avoided in new code. React 16.3 introduced newer lifecycle methods that enhance performance and better align with modern development practices. Developers are encouraged to adopt these newer methods to ensure compatibility with future versions of React.

Transition to useEffect Hook

After understanding the lifecycle methods, let's transition to discussing the modern useEffect hook. This hook simplifies handling side effects in functional components, marking a significant shift from class component lifecycle methods to hooks in functional components. The useEffect hook consolidates the capabilities of several lifecycle methods, providing a more unified and efficient way to manage side effects.

By embracing the new lifecycle methods and hooks like useEffect, developers can write cleaner, more maintainable React code that is ready for the future developments in the framework.

Understanding the React useEffect Hook

The React useEffect Hook is a way to add lifecycle methods to a functional component. It allows us to run side effects. 

Side effects are anything that affects the state of the application outside of the component, (e.g. fetching data from an API, setting up event listeners, updating the DOM) in a declarative way, without needing to use class components and the traditional lifecycle methods.

The purpose of the useEffect hook is to allow functional components to have access to these side effects in a way that is similar to lifecycle methods in class components. The basic syntax of the useEffect hook: 

useEffect(() => {
    // side effect code goes here
}, [dependency1, dependency2, ...]); 

The first argument to useEffect is a function that contains the side effect code we want to run. The second argument is an optional array of dependencies, which tell React when the effect should run. If any of the dependencies change, the effect will run again.

Let’s try to understand the usage of the useEffect hook with some quick examples:

Fetching data from an API Example:

import React, { useState, useEffect } from "react";
function ZipyComponent() {
  const [data, setData] = useState(null);

  useEffect(() => {
    async function fetchData() {
      const response = await fetch("https://example.com/api/data");
      const json = await response.json();
      setData(json);
    }
    fetchData();
  }, []);

  if (!data) {
    return <div>Loading...</div>;
  }
  return (
    <div>
      <h1>Data from API</h1>
      <ul>
        {data.map((item) => (
          <li key={item.id}>{item.name}</li>
        ))}
      </ul>
    </div>
  );
}

In this example, we’re using the useEffect hook to fetch data from an API and update the state of a component in a functional component. The useState hook is also used to initialize the data state to null. 

The useEffect hook is called with a function that fetches the data using async/await and updates the state with setData. The dependency array [] ensures that the effect only runs once when the component mounts.

If the data state is null, the component will render a "Loading..." message. Once the data is fetched, the component will render a list of items with the map function. The key attribute is used to identify each item in the list. This example demonstrates how the useEffect hook can be used to fetch and update data in a functional component.

Setting up & cleaning up event listeners:

import React, { useState, useEffect } from "react";

function ZipyComponent() {
  const [count, setCount] = useState(0);

  useEffect(() => {
    function handleKeyPress(event) {
      if (event.key === "ArrowUp") {
        setCount(count + 1);
      }
    }
    document.addEventListener("keydown", handleKeyPress);
    return () => {
      document.removeEventListener("keydown", handleKeyPress);
    };
  }, [count]);
  return (
    <div>
      <h1>Count: {count}</h1>
    </div>
  );
}

We’re using useEffect hook here to add and remove an event listener. In this example, the event listener listens for the keydown event and increments the count state when the up arrow is pressed.

The useEffect hook is used with an empty dependency array so that the effect is only run once when the component mounts. The hook also returns a cleanup function that removes the event listener when the component unmounts. This ensures that the event listener is only active when the component is mounted and avoids memory leaks.

Updating the DOM:

import React, { useState, useEffect } from "react";

function ZipyComponent() {
  const [count, setCount] = useState(0);

  useEffect(() => {
    document.title = `Count: ${count}`;
  }, [count]);

  return (
    <div>
      <h1>Count: {count}</h1>
      <button onClick={() => setCount(count + 1)}>Increment</button>
    </div>
  );
}

In this example, we utilize the useState hook to manage the count state, and useEffect to update the document title to reflect the current count whenever it changes. By including [count] as the second argument to useEffect, we ensure that the effect is triggered each time the count state is altered.

When the user presses the "Increment" button, the state of count is updated, prompting the useEffect hook to execute again. The hook then updates the document title with the new count, which is visible in the browser tab. This demonstrates how useEffect can be effectively used to update the DOM in reaction to state changes.

useEffect considerably simplifies handling side effects in functional components compared to traditional class components, where side effects were managed using lifecycle methods. This could often make the code more complex and challenging to maintain. useEffect offers a more declarative and intuitive approach to managing side effects, making it easier to understand and predict the behavior of a component. Overall, it streamlines the process of managing side effects in React, enhancing accessibility for developers to craft and comprehend intricate applications.

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Dependencies of useEffect and how to handle them

As we learned before, in React's useEffect Hook, dependencies are used to determine when the effect should be executed. If any of the dependencies have changed since the last render, the effect will be executed again. 

The dependencies are passed as an array to the useEffect Hook and can include state variables, props, and functions. Let’s see this in action:

import React, { useState, useEffect } from "react";

function ZipyComponent({ initialCount }) {
  const [count, setCount] = useState(initialCount);

  useEffect(() => {
    console.log("Count changed:", count);
  }, [count]);

  return (
    <div>
      <h1>Count: {count}</h1>
      <button onClick={() => setCount(count + 1)}>Increment</button>
    </div>
  );
}

In this example, we are using the count state variable as a dependency for the useEffect Hook. Whenever the count variable changes, the effect will be executed, and the message "Count changed:" along with the new count value will be logged to the console.

To handle dependencies in useEffect, there are a few things to keep in mind:

  • If we don't provide any dependencies to useEffect, the effect will run after every render.
  • If we provide an empty array as the dependencies, the effect will only run once when the component mounts.
  • If we provide dependencies to useEffect, make sure they are complete and stable. If we only include a subset of the dependencies, the effect may not run when you expect it to.
  • If we need to access a value inside the effect that is defined outside of the effect (like a prop), we can include it as a dependency to ensure the effect runs when that value changes.

Using useEffect Hook to apply lifecycle methods

In functional components, the useEffect Hook can be used to replicate the functionality of the traditional lifecycle methods. The useEffect Hook is called after every render of the component and can perform any side effect, such as modifying the DOM or fetching data from an API. 

By using the second argument of the useEffect Hook, we can control when it should be called based on specific dependencies. Let’s understand this in greater detail with some examples:

componentDidMount equivalent:

In class components, the componentDidMount() method is called after the component has been mounted in the DOM. 

To replicate this behavior in functional components, we can use the useEffect Hook with an empty array as the second argument. This will ensure that the effect is only run once after the component has been mounted.
Example:

import React, { useState, useEffect } from "react";

function ZipyComponent() {
  const [data, setData] = useState(null);

  useEffect(() => {
    async function fetchData() {
      const response = await fetch("https://example.com/api/data");
      const json = await response.json();
      setData(json);
    }
    fetchData();
  }, []);

  return (
    <div>
      {data ? (
        <ul>
          {data.map((item) => (
            <li key={item.id}>{item.name}</li>
          ))}
        </ul>
      ) : (
        <div>Loading...</div>
      )}
    </div>
  );
}

In this example, useEffect will only run once when the component mounts because the dependency array is empty. fetchData is an async function that fetches data from an API and updates the state using setData.

componentDidUpdate equivalent:

In class components, the componentDidUpdate method is called after the component has been updated with new props or states.

To replicate this behavior in functional components, we can use the useEffect Hook with the appropriate dependencies listed as the second argument. This will ensure that the effect is only run when the listed dependencies have changed.
Example:

import React, { useState, useEffect } from "react";

function ZipyComponent(props) {
  const [count, setCount] = useState(props.initialCount);

  useEffect(() => {
    document.title = `Count: ${count}`;
  }, [count]);

  function handleClick() {
    setCount(count + 1);
  }

  return (
    <div>
      <h1>Count: {count}</h1>
      <button onClick={handleClick}>Increment</button>
    </div>
  );
}

In this example, useEffect will run every time count changes because the count is listed as a dependency in the array. The effect updates the document title to include the current count.

componentWillUnmount equivalent:

In class components, the componentWillUnmount method is called before the component is unmounted from the DOM.

To replicate this behavior in functional components, we can return a cleanup function from the useEffect Hook. This function will be called before the component is unmounted.
Example:

import React, { useState, useEffect } from "react";

function ZipyComponent() {
  const [count, setCount] = useState(0);

  useEffect(() => {
    function handleKeyPress(event) {
      if (event.key === "ArrowUp") {
        setCount(count + 1);
      }
    }
    document.addEventListener("keydown", handleKeyPress);
    return () => {
      document.removeEventListener("keydown", handleKeyPress);
    };
  }, [count]);

  return (
    <div>
      <h1>Count: {count}</h1>
    </div>
  );
}

In this example, useEffect sets up a mousemove event listener when the component mounts. The return function removes the event listener when the component unmounts. This ensures that the event listener is only active when the component is mounted and avoids potential memory leaks.

Overall, using the useEffect Hook with lifecycle methods allows us to manage state and side effects in functional components in a similar way to class components, without having to write boilerplate code. It can help to make the code more concise and easier to understand.

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Wrapping up

React's useEffect hook is a powerful and flexible way to add side effects to the functional components. It allows us to manage state and perform side effects in a more concise and declarative way, without the need for class components and traditional lifecycle methods.

With useEffect, we have fine-grained control over when side effects are executed and when they are cleaned up. But with this control comes the problem with debugging errors, especially when fetching data from APIs. To overcome this you can use Zipy which is an intelligent debugging and error-monitoring tool designed for ReactJS applications. 

With Zipy, you can easily monitor your component's state and quickly identify and resolve errors in your code. It provides detailed stack traces that help you pinpoint errors and resolve them quickly.

Overall, useEffect provides a simple and elegant solution to the problem of managing side effects in React. By understanding how to use lifecycle methods in functional components, we can write more maintainable, readable, and scalable code for React applications.

Set up Zipy and start tracking React errors:

  1. Visit https://app.zipy.ai/sign-up to get the project key.
  2. Install Zipy via script tag or npm. window.zipy.init() must be called client-side, not server-side.

Script Tag:

    
// Add to your HTML:<script src="https://cdn.zipy.ai/sdk/v1.0/zipy.min.umd.js" crossorigin="anonymous"></script><script> window.zipy && window.zipy.init('Project SDK Key');</script>

NPM:

    
npm i --save zipyai
    
//Code:import zipy from 'zipyai'; zipy.init('Project SDK Key');

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