useEffect Hook

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Manage with your component's lifecycle with the useEffect hook

React Hooks Handbook

Intro to React Hooks

3:39

Create your first React app

4:23

React Component

2:54

Styling in React

5:06

Styles and Props

2:22

Understanding Hooks

3:21

useState Hook

2:54

useEffect Hook

3:41

useRef Hook

3:00

Props

3:11

Conditional Rendering

4:21

Load Local Data

4:04

Fetch Data from an API

5:40

Toggle a state

4:05

useInput Hook

6:04

Gatsby and React

6:44

NextJS and React

5:24

React TypeScript Part 1

8:19

React TypeScript Part 2

7:35

useScrollPosition Hook

4:26

useOnScreen hook

8:08

useContext Hook

8:32

Fragments

2:43

Lazy Loading

4:05

React Suspense

3:13

Environment Variables

4:43

Reach Router

5:31

URL Params

4:04

SEO and Metadata

6:47

Favicon

3:03

Dynamic Favicon

2:14

PropTypes

3:54

Custom PropTypes

3:58

useMemo Hook

4:05

forwardRef Hook

3:28

Handling Events

5:44

Spread attributes

3:35

useMousePosition Hook

4:55

useReducer with useContext Part 1

7:33

useReducer with useContext Part 2

6:48

useReducer with useContext Part 3

5:43

Netlify

5:08

Gatsby Cloud

6:19

Gatsby Plugin Image

8:11

useOnClickOutside Hook

6:32

useWindowSize Hook

4:14

usePageBottom hook

4:48

useLocalStorage Hook

5:27

Three.js in React Part 1

17:33

Three.js in React Part 2

11:18

CodeSandbox link

You can find the full code for this tutorial at https://codesandbox.io/s/useeffect-yuwht.

Understanding the component lifecycle

Using the useEffect hook means understanding the lifecycle of the component. This lifecycle consists of three main parts: mounting, updating, and unmounting. If you're familiar with the old wait to deal with the component lifecycle, these three parts correspond to ComponentDidMount, ComponentDidUpdate, ComponentWillUnmount.

To understand better a component's lifecycle, we can look at the lifecycle of a flower. When the flower's seed is planted, it is mounted. Then, as it grows, it is updating and, unfortunately, it will die (or unmount) someday. The component's lifecycle is exactly the same: when the user lands on the page, the component is mounted, then as the states update, the component is also updated, and, finally, the component is unmounted when the user leaves the page.

Anatomy of the useEffect hook

The component lifecycle is represented in three different parts of the useEffect hook, as shown in the code snippet below.

useEffect(() => {
    // Mounting

    return () => {
        // Cleanup function
    }
}, [//Updating])

The first part is the mounting part. That's when the component is initially rendered when the user lands on the page. The return function is the cleanup function, or when the user leaves the page and the component will unmount. The array is the last part, and it is where you put the states that will update throughout the component's lifecycle. You can discard the array if your component won't update during its lifecycle.

When to use the useEffect hook?

The useEffect hook is useful when you wish to run some functions during the component's lifecycle. For example, if you want to update the UI when a state changes, the useEffect hook is the way to go. You can also define a state on first load (when componentDidMount), and also clean the state when the component is unmounting (componentWillUnmount).

Let's look at an example below. We want to update the page title every time the user clicks on a button on the page, using the useEffect and useState hooks.

Create your component

Start by creating your component. We'll reuse the button component we created in the useState hook section and incorporate the useEffect hook as well.

import React, { useState } from "react"

const Button = () => {
    const [count, setCount] = useState(0)

    return <button onClick={() => setCount(count + 1)}>You clicked {count} times</button>;
}

export default Button

Import useEffect

In order to use useEffect, you'll need to import it at the top of the file. Don't forget to keep React and useState as we still need them.

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

Define useEffect

Next, create a new useEffect just above the return statement in your component. We want to update the document title every time the user clicks on the button, so let's set it in the mounting part of the useEffect hook.

useEffect(() => {
		document.title = `You clicked ${count} times.` // This is the mounting part
}, [])

You'll see the title of the tab change to You clicked 0 times, since the value of count is initially set to 0.

However, when you click on the button, the text on the button updates but not the title of the tab. Therefore, we need to add the count state in the update array of the useEffect hook. Every time the count is updated, the useEffect will be re-run, updating the document title in our case.

useEffect(() => {
		document.title = `You clicked ${count} times.`
}, [count]) // Add the count state in the array here

Now, every time you click on the button, the title of the tab will update to reflect the number of times the user clicked on the button.

Final code with styling

You can style your components by using the styled-components package in your project. Learn more about it in the Styling in React section of this handbook.

The final code incorporating useEffect as well as useState and styled-components will look like this:

import React, { useState, useEffect } from "react";
import styled from "styled-components";

const MyButton = () => {
    const [count, setCount] = useState(0);

    useEffect(() => {
        document.title = `You clicked ${count} times`;
    }, [count]);

    return (
        <StyledButton onClick={() => setCount(count + 1)}>
            You clicked {count} times
        </StyledButton>
    );
};

export default MyButton;

const StyledButton = styled.button`
    background: linear-gradient(91.4deg, #2fb8ff 0%, #9eecd9 100%);
    padding: 12px 0;
    width: 200px;
    border: none;
    border-radius: 30px;
    color: white;
    font-weight: bold;
    font-family: Segoe UI, sans-serif;
`;

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Intro to React Hooks

An overview of React Hooks and the frameworks you can use to build your React application blazingly fast

3:39

Create your first React app

Create your first React project from the Terminal and save it on your local computer

4:23

React Component

Create your first JSX component using React

2:54

Styling in React

How to style your React components using inline styling, separate stylesheets or styled-components

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Styles and Props

Render different styles depending on different properties passed to your component

2:22

Understanding Hooks

Learn about the basics of React Hooks, which introduced at React Conf 2018

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useState Hook

Use the useState hook to manage local state in your React component

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useEffect Hook

Manage with your component's lifecycle with the useEffect hook

3:41

useRef Hook

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Props

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Render different UIs depending on different conditions and states

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Load Local Data

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Fetch Data from an API

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Create a static content-oriented website using React on Gatsby

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NextJS and React

Create your first NextJS React application

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React TypeScript Part 1

Learn how to create a React TypeScript application using the Create React App, Gatsby and NextJS methods

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React TypeScript Part 2

Learn the basics of TypeScript and how to use TypeScript in a React component

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useScrollPosition Hook

Create a custom hook to listen to the current window position of the user

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useOnScreen hook

Create a custom hook to listen to when an element is visible on screen

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useContext Hook

Manage global states throughout the entire application

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Fragments

Group multiple children together with React Fragments

2:43

Lazy Loading

Lazy Load heavy components to improve performance

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React Suspense

Wait for data with React Suspense and React.lazy

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Environment Variables

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Reach Router

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URL Params

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Dynamic Favicon

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useMemo Hook

Prevent unnecessary re-renders when the component stays the same

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forwardRef Hook

Forward a ref to a child component

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Handling Events

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Spread attributes

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useMousePosition Hook

Detect the user's mouse position on a bound element

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useReducer with useContext Part 1

Create a reducer to be used in a context

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useReducer with useContext Part 2

Incorporate useReducer with useContext

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useReducer with useContext Part 3

Connect the context and reducer with the frontend

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Netlify

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Gatsby Cloud

Deploy to production using Gatsby Cloud

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useOnClickOutside Hook

Toggle a modal visibility with a useOnClickOutside hook

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useWindowSize Hook

Create a hook to determine the width and height of the window

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usePageBottom hook

Detect if the user scrolled to the bottom of the page

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useLocalStorage Hook

Store an item in a browser's local storage

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Three.js in React Part 1

Bring your website to life with beautiful 3D objects

17:33

Three.js in React Part 2

Bring your website to life with beautiful 3D objects

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