Discover the power of React's useEffect() hook for managing side effects efficiently. Learn its usage for data fetching, event handling & more.byHasanul Haque Banna

React useEffect() Hook: A Simple Guide to Usage and Benefits

Hello, fellow readers! React, the popular JavaScript library for building user interfaces offers a wide array of tools and features to make web development more efficient and enjoyable. One of the essential hooks in React is the useEffect() hook, which allows developers to manage side effects in their applications.

The useEffect() hook in React is used to perform side effects in functional components. It allows you to run code in response to certain conditions or events, such as when the component mounts or when a specific variable changes. In this article, we'll explore the basic usage of the useEffect() hook and discuss when and how to use it effectively.

Understanding the useEffect() Hook

The useEffect() hook is part of the React Hooks API, introduced in React 16.8. It is designed to handle side effects in functional components. Side effects refer to operations that occur outside the standard component rendering process, such as data fetching, DOM manipulation, and subscriptions.

The useEffect() hook takes two arguments: a function and an optional dependency array. The function is executed after every render, and its purpose is to perform the desired side effects. The optional dependency array contains variables that the effect depends on, ensuring that the effect runs only when these dependencies change.

Basic Usage

To get started with the useEffect() hook, you need to import it from the 'React' library. Here's a simple example of how to use it:

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

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

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

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

In this example, we have a functional component MyComponent that manages a count variable using the useState hook. We use the useEffect() hook to update the document title with the current count value, and we specify the dependency array as [count]. This means that the effect will run whenever the count variable changes.

When to use useEffect():

Here are some scenarios when you may want to use the useEffect() hook:

Data fetching: You can use useEffect() to fetch data from an API when the component mounts and update the component state accordingly.

Subscribing to events: useEffect() can be used to subscribe to events, such as keyboard or mouse events, and perform actions in response to those events.

Updating document title: You can use useEffect() to update the document title dynamically based on the component state or props.

Cleaning up resources: If your component uses any external resources, such as timers or subscriptions, you can clean them up using the cleanup function returned by useEffect().

How to use useEffect():

The useEffect() hook takes two arguments: a function that represents the side effect code and an optional array of dependencies.

The side effect function is executed after the component renders. It can perform any asynchronous or synchronous operations you need.

The dependencies array specifies the variables that the effect depends on. If any of these variables change, the effect will be re-executed. If the array is empty, the effect will only run once (on mount) and clean up on unmount.

Here's an example that demonstrates using the useEffect() hook with a dependency array:

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

function MyComponent({ userId }) {
  const [user, setUser] = useState(null);

  useEffect(() => {
    // Fetch user data from API based on userId
      .then(response => response.json())
      .then(data => setUser(data));

    // Cleanup code (optional)
    return () => {
      // Cancel any pending requests or cleanup resources
  }, [userId]); // Specify userId as the dependency

  // ...

In this example, the useEffect() hook will fetch user data whenever the userId prop changes. The function returned by useEffect() will cancel any pending requests or clean up resources when the component unmounts or when userId changes.

I hope this helps you understand the basic usage, when, and how to use the useEffect() hook in React! Let me know if you have any further questions.


The useEffect() hook is a fundamental tool in React for managing side effects in functional components. By understanding its basic usage and following best practices, you can use it effectively in your projects. Whether you're fetching data, manipulating the DOM, managing subscriptions, or cleaning up resources, the useEffect() hook empowers you to build powerful and responsive web applications in React.