Full Stack Developer Course

ReactJS Introduction

What is ReactJS? Features, Uses, Benefits, Full Introduction

Full History of ReactJS (With React Versions History)

React Environment Setup & Working

How Does ReactJS Work?

How to Setup ReactJS Development Environment? Step by Step

ReactJS Directory Structure and Workflow of React App

React JSX

What is ReactJS JSX? Characteristics, Advantages, Disadvantages

ReactJS ES, NPM, and Babel Explained With Examples

What is ReactJS DOM? Virtual DOM, DOM Router, Methods, How to Install?

What is ReactJS Code Splitting? How Does React Code Splitting Work?

What Are ReactJS Lists? Explained in Simple Terms

What Are Keys in ReactJS? What is Key Uniqueness?

ReactJS Rendering Elements: How to Render Element in React?

ReactJS Conditional Rendering Explained With Example

ReactJS Transition Group: react-transition-group With Example

What Are ReactJS Forms? How to Create Forms in ReactJS?

ReactJS API and AJAX Explained in Simple Terms

Refs in ReactJS

What are React Refs? When to & When Not To Use Refs?

How to Create and Add React Refs?

React Components

What are Components & their types in ReactJs

What are Functional Components in ReactJS?

Understanding ReactJS Component Lifecycle

Difference between Functional and Class Components in ReactJs

Difference between React Presentational and Container Components

React Props

What are ReactJS Props?  | Methods as Props

Understanding Different  PropTypes in  ReactJs

Understanding How State work in ReactJS

Implementation of State and Lifecycle in ReactJS

ReactJS Hooks

What Are ReactJS Hooks? Explained

Understanding ReactJs useState Hook

Understanding ReactJs useEffect Hook

Understanding ReactJs Context

ReactJS Routers

Introduction to ReactJs Routers and Routing

Different Types of Routers in ReactJS

Understanding ReactJS Fragments and its uses

ReactJS - Certificate

<h2 dir="ltr">Benefits of ReactJS Tutorial for Beginners</h2>
<p dir="ltr">There are many benefits of this tutorial on ReactJS, including:</p>
<ul>
<li dir="ltr">
<h3>Learning a popular and in-demand technology</h3>
</li>
</ul>
<p dir="ltr">ReactJS is a widely-used technology that is in high demand among employers. Learning it can help you become more employable and increase your job prospects.</p>
<ul>
<li dir="ltr">
<h3>Building a strong foundation&nbsp;</h3>
</li>
</ul>
<p dir="ltr">The ReactJS tutorial can help you build a strong foundation of knowledge and skills in this technology, which can be applied to real-world projects.</p>
<ul>
<li dir="ltr">
<h3>Developing problem-solving skills</h3>
</li>
</ul>
<p dir="ltr">ReactJS is a complex technology that requires critical thinking and problem-solving skills. By working through a tutorial, you can develop these skills and become more proficient in using it.</p>
<ul>
<li dir="ltr">
<h3>Improving coding skills</h3>
</li>
</ul>
<p dir="ltr">ReactJS is a JavaScript library, which means that learning it can help you improve your overall coding skills, including knowledge of JavaScript, HTML, and CSS.</p>
<ul>
<li dir="ltr">
<h3>Access to a structured learning environment</h3>
</li>
</ul>
<p dir="ltr">The React tutorial provides you with a structured learning environment that helps you learn ReactJS in a logical and organized way, with clear explanations and examples.</p>
<ul>
<li dir="ltr">
<h3>Access to helpful resources</h3>
</li>
</ul>
<p dir="ltr">Our ReactJS tutorials include resources such as video sessions, quizzes, and interview questions, which help you gain a deeper understanding of the technology.</p>
<ul>
<li dir="ltr">
<h3>Flexibility and convenience</h3>
</li>
</ul>
<p dir="ltr">The tutorial on React can be accessed from anywhere with an internet connection, making it a flexible and convenient way for beginners to learn.</p>
<h2 dir="ltr">Why learn ReactJS in 2025?</h2>
<ul>
<li dir="ltr">
<h3>Popularity</h3>
</li>
</ul>
<p dir="ltr">ReactJS is one of the most popular and widely-used JavaScript libraries, with a large and active community of developers. As a result, learning ReactJS can open up a wide range of job opportunities and career paths.</p>
<ul>
<li dir="ltr">
<h3>Versatility</h3>
</li>
</ul>
<p dir="ltr">ReactJS can be used for a wide variety of applications, including web development, mobile app development, and even desktop app development. This makes it a versatile technology to learn that can be applied to many different projects and industries.</p>
<ul>
<li dir="ltr">
<h3>Efficiency</h3>
</li>
</ul>
<p dir="ltr">It is designed to be efficient and fast, which makes it an excellent choice for building high-performance applications. This can be particularly beneficial for businesses and organizations that need to deliver fast and responsive applications to their customers.</p>
<ul>
<li dir="ltr">
<h3>Scalability</h3>
</li>
</ul>
<p dir="ltr">ReactJS is scalable, which means that it can be used to build applications of all sizes, from small personal projects to large enterprise applications. This makes it an ideal technology for developers who want to build applications that can grow and evolve over time.</p>
<ul>
<li dir="ltr">
<h3>Modular architecture</h3>
</li>
</ul>
<p dir="ltr">ReactJS uses a modular architecture, which makes it easy to break down large applications into smaller, more manageable components. This can make development faster and more efficient, as developers can work on individual components in isolation.</p>
<h2 dir="ltr">Applications and Uses of ReactJS</h2>
<p dir="ltr">ReactJS is a versatile front-end development tool that can be used for a wide variety of applications.&nbsp;</p>
<ul>
<li dir="ltr">
<h3>Single-page applications (SPAs)</h3>
</li>
</ul>
<p dir="ltr">ReactJS is well-suited for building SPAs, which are web applications that load a single HTML page and dynamically update the content as the user interacts with the application. ReactJS is particularly well-suited for building SPAs that require real-time updates and interactive features.</p>
<ul>
<li dir="ltr">
<h3>Progressive web applications (PWAs)</h3>
</li>
</ul>
<p dir="ltr">ReactJS can be used to build PWAs, which are web applications that have native app-like functionality, such as offline caching, push notifications, and home screen icons. PWAs are becoming increasingly popular as they provide a better user experience and improved performance compared to traditional web applications.</p>
<ul>
<li dir="ltr">
<h3>Mobile applications</h3>
</li>
</ul>
<p dir="ltr">ReactJS can be used to build mobile applications for iOS and Android using tools like React Native. React Native allows developers to build mobile applications using ReactJS syntax, which can significantly reduce development time and costs.</p>
<ul>
<li dir="ltr">
<h3>Enterprise applications</h3>
</li>
</ul>
<p dir="ltr">ReactJS is well-suited for building large, complex enterprise applications, as it supports modular architecture, which allows developers to break down large applications into smaller, more manageable components.</p>
<ul>
<li dir="ltr">
<h3>E-commerce websites</h3>
</li>
</ul>
<p dir="ltr">ReactJS can be used to build e-commerce websites that require real-time updates and interactive features, such as shopping carts, product filters, and recommendations.</p>
<h2 dir="ltr">Learning Fundamentals of ReactJS</h2>
<p dir="ltr">ReactJS is an open-source JavaScript library used for building user interfaces. Developed by Facebook, ReactJS has become one of the most popular front-end development frameworks, known for its speed, efficiency, and scalability.</p>
<p dir="ltr">At its core, ReactJS is designed to simplify the process of building complex user interfaces by breaking them down into smaller, reusable components. These components can be combined to create more complex applications, making development faster, more efficient, and easier to maintain.</p>
<p dir="ltr">One of the key features of ReactJS is its use of a virtual DOM (Document Object Model), which is a lightweight representation of the actual DOM. When changes are made to the virtual DOM, ReactJS efficiently updates only the parts of the actual DOM that have been changed, rather than re-rendering the entire page. This results in faster rendering and a more responsive user experience.</p>
<p dir="ltr">ReactJS also supports server-side rendering, which means that pages can be rendered on the server before being sent to the browser. This can improve performance and make it easier to implement SEO best practices.</p>
<p dir="ltr">ReactJS is often used in conjunction with other front-end development technologies, such as Redux, a state management library, and React Router, a library for handling routing in ReactJS applications.</p>
<h2 dir="ltr">Latest React Tutorial 2025</h2>
<p dir="ltr">With so many resources available online, it can be challenging to find a reliable and up-to-date ReactJS tutorial 2025 that covers all the essential concepts in a simple and easy-to-understand manner.</p>
<p dir="ltr">You might have spent countless hours searching for the right tutorial, only to end up feeling confused and overwhelmed by the vast amount of information available.</p>
<p dir="ltr">Our React tutorial for beginners is the perfect solution for your learning needs. It covers all the concepts from the basics to the advanced level, and it includes syntax, code, program examples, video sessions, quizzes, interview questions, and more.</p>
<h2 dir="ltr">Prerequisites to Learn ReactJS</h2>
<p dir="ltr">Before learning ReactJS, it is recommended to have a strong foundation in web development technologies like HTML, CSS, and JavaScript.</p>
<p dir="ltr"><em><strong>Note</strong>: While these are not strict prerequisites, having a basic understanding of these technologies will help you learn ReactJS more efficiently.</em></p>
<ul>
<li dir="ltr">
<h3>HTML</h3>
</li>
</ul>
<p dir="ltr">Knowledge of HTML is essential for building the structure and layout of web pages. You should be familiar with HTML tags, attributes, and elements.</p>
<ul>
<li dir="ltr">
<h3>CSS</h3>
</li>
</ul>
<p dir="ltr">Understanding CSS is important for styling web pages. You should be familiar with CSS properties, selectors, and media queries.</p>
<ul>
<li dir="ltr">
<h3>JavaScript</h3>
</li>
</ul>
<p dir="ltr">Since React has been built on JS, individuals having its knowledge can easily grasp the concepts. You should be comfortable with JavaScript concepts like variables, data types, functions, objects, and arrays.</p>
<ul>
<li dir="ltr">
<h3>ES6</h3>
</li>
</ul>
<p dir="ltr">ES6 is the latest version of JavaScript, and it introduced several new features like arrow functions, classes, modules, and destructuring. Knowledge of ES6 is important for writing modern ReactJS code.</p>
<ul>
<li dir="ltr">
<h3>Node.js and npm</h3>
</li>
</ul>
<p dir="ltr">Node.js is a server-side JavaScript runtime, and npm is a package manager for Node.js. You will need to install Node.js and npm to work with ReactJS.</p>
<h2 dir="ltr">Practice With ReactJS Quiz</h2>
<p dir="ltr">We have also created several quizzes for you to practice and test your knowledge and skills.</p>
<p dir="ltr"><a href="https://www.tutorialsfreak.com/reactjs-tutorial/quizzes">ReactJS Quiz</a></p>
<h2 dir="ltr">Get Started With ReactJS Tutorial (Learn Step by Step With Examples)</h2>
<p dir="ltr">In addition to learning ReactJS, our tutorial will help you build your career in this field, as ReactJS is widely used in the development of web applications and mobile apps.&nbsp;</p>
<p dir="ltr">This is a ReactJS tutorial from scratch and step by step, so you'll have the necessary knowledge and skills to become a proficient React Developer and land your dream job.</p>
<p dir="ltr">So, whether you're a beginner or an experienced developer, this tutorial is the perfect resource to learn ReactJS and build your career in this exciting field.&nbsp;</p>
<h2 dir="ltr">FAQs Related to ReactJS Tutorial</h2>
<p dir="ltr">Here are some frequently asked questions (FAQs) related to ReactJS:</p>
<h3 dir="ltr">1. What is ReactJS, and what is it used for?</h3>
<p dir="ltr">ReactJS is an open-source JavaScript library used for building user interfaces. It is used to simplify the process of building complex user interfaces by breaking them down into smaller, reusable components.</p>
<h3 dir="ltr">2. What is JSX?</h3>
<p dir="ltr">JSX is a syntax extension used with ReactJS that helps in writing HTML-like code within JavaScript. It simplifies the process of creating user interfaces by allowing developers to write both HTML and JavaScript in the same file.</p>
<h3 dir="ltr">3. What is a component in ReactJS?</h3>
<p dir="ltr">A component in ReactJS is a reusable piece of code that defines a part of a user interface. Components can be combined to create more complex interfaces, and can be easily reused across different parts of an application.</p>
<h3 dir="ltr">4. What is the difference between props and state in ReactJS?</h3>
<p dir="ltr">Props (short for properties) are used to pass data from one component to another, while state is used to manage data within a component. Props are read-only and cannot be modified by the component that receives them, while state can be modified using the setState() method.</p>
<h3 dir="ltr">5. What is Redux, and how is it used with ReactJS?</h3>
<p dir="ltr">Redux is a state management library that can be used with ReactJS to manage the application state. It allows developers to create a global store that holds all of the application's state, and can be easily accessed and modified by any component within the application.</p>
<h3 dir="ltr">6. What is React Native?</h3>
<p dir="ltr">React Native is a framework used to build mobile applications for iOS and Android using ReactJS syntax. It allows developers to build native mobile applications using familiar web development tools and techniques.</p>
<h3 dir="ltr">7. What is a ReactJS tutorial?</h3>
<p dir="ltr">A ReactJS tutorial is a step-by-step guide that teaches how to build web applications using the ReactJS library. It covers the basics of ReactJS, including components, JSX, props, state, and more advanced topics such as Redux, server-side rendering, and testing.</p>
<h3 dir="ltr">8. Who is a ReactJS tutorial for?</h3>
<p dir="ltr">A ReactJS tutorial is intended for anyone who wants to learn how to build web applications using ReactJS. It is particularly useful for beginners who have a basic understanding of HTML, CSS, and JavaScript.</p>
<h3 dir="ltr">9. How long does it take to complete the ReactJS tutorial?</h3>
<p dir="ltr">The length of time it takes to complete our React tutorial depends on your learning pace. Some people may take a few days to complete, while others may take several days or weeks.</p>
<h2 dir="ltr">Career Opportunities in ReactJS</h2>
<p dir="ltr">ReactJS has gained immense popularity and has become one of the most widely used front-end web development frameworks. As a result, there are plenty of career opportunities available for ReactJS developers.&nbsp;</p>
<ul>
<li dir="ltr">
<h3>React Developer</h3>
</li>
</ul>
<p dir="ltr">A React Developer is responsible for developing user-friendly web applications using ReactJS. The role involves writing clean and maintainable code, designing user interfaces, and working closely with the design and back-end teams.</p>
<ul>
<li dir="ltr">
<h3>Front-End Developer</h3>
</li>
</ul>
<p dir="ltr">A Web Developer who is responsible for building the front-end or user-facing side of a website or web app. React is among the most popular front-end web development frameworks, and knowledge of ReactJS is highly valued in this role.</p>
<ul>
<li dir="ltr">
<h3>Full-Stack Developer</h3>
</li>
</ul>
<p dir="ltr">A Web Developer who is responsible for developing both the front-end and back-end of a website or web app. React is often used in conjunction with other back-end frameworks and libraries, making it a valuable skill for Full-Stack Developers.</p>
<h2 dir="ltr">Want to Learn Complete MERN Stack With Live Training?</h2>
<p dir="ltr">MERN stands for MongoDB, ExpressJS, ReactJS, and NodeJS. It makes the complete full-stack development.</p>
<p dir="ltr">If you want to learn it from industry experts, then you can go for the <a href="https://www.wscubetech.com/online-mern-stack-developer-course-india.html">MERN Stack Course</a> by WsCube Tech!</p>
<p dir="ltr">&nbsp;</p>
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<p dir="ltr">Are you looking to learn ReactJS and build a strong foundation in this popular JavaScript library? Look no further! Our comprehensive ReactJS tutorial covers everything from the basics to advanced concepts in a simple and easy-to-understand manner. Whether you're a beginner looking to get started with React or a web developer looking to sharpen your skills, this tutorial has something for everyone.</p>
<p dir="ltr">With our tutorial on React, you'll get access to easy-to-follow syntax, code examples, program demonstrations, video sessions, quizzes, and interview questions, ensuring that you learn ReactJS in a comprehensive and structured way. You'll also get hands-on practice and opportunities to apply your skills with coding exercises.</p>
<p dir="ltr">Our tutorial is specifically designed to cater to beginners, so no prior knowledge of ReactJS is required. However, experienced React Developers can also find useful resources in it to enhance their skills.</p>

ReactJS - Example

ReactJS Tutorial for Beginners (Learn React The Easy Way)

ReactJS Tutorial

ReactJS Quiz Test (Free ReactJS MCQ Online)

Make yourself future-ready in web development by learning ReactJS.

ReactJS Tutorial for Beginners

What is useEffect Hook in ReactJS?

How does the React useEffect hook work?

Test your knowledge with a quick quiz!

<p style="text-align: justify;">The main purpose of using <strong>useEffect Hook </strong>is to allow you to perform side effects in your components. For example, tasks like updating the <a href="https://www.tutorialsfreak.com/reactjs-tutorial/understanding-reactjs-dom" target="_blank" rel="noopener"><strong>DOM</strong></a>, fetching data from API end-points, setting up timers or subscriptions.&nbsp;</p>

<p style="text-align: justify;">It accepts two arguments. The second argument is optional.</p>
<p style="text-align: justify;"><em>useEffect(, )</em></p>
<p style="text-align: justify;">Let&rsquo;s consider an example for setting up timers.</p>
<p style="text-align: justify;"><code><em>import { useState, useEffect } from "react";</em></code></p>
<p style="text-align: justify;"><code><em>import ReactDOM from "react-dom";</em></code></p>
<p style="text-align: justify;"><code><em>function Timer() {</em></code></p>
<p style="text-align: justify;"><code><em>&nbsp;&nbsp;const [count, setCount] = useState(0);</em></code></p>
<p style="text-align: justify;"><code><em>&nbsp;&nbsp;useEffect(() =&gt; {</em></code></p>
<p style="text-align: justify;"><code><em>&nbsp;&nbsp;&nbsp;&nbsp;setTimeout(() =&gt; {</em></code></p>
<p style="text-align: justify;"><code><em>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;setCount((count) =&gt; count + 1);</em></code></p>
<p style="text-align: justify;"><code><em>&nbsp;&nbsp;&nbsp;&nbsp;}, 1000);</em></code></p>
<p style="text-align: justify;"><code><em>&nbsp;&nbsp;});</em></code></p>
<p style="text-align: justify;"><code><em>&nbsp;&nbsp;return</em></code></p>
<p style="text-align: justify;">&nbsp;</p>
<h1>I've rendered {count} times</h1>
<p style="text-align: justify;">&nbsp;</p>
<p style="text-align: justify;"><code><em>;</em></code></p>
<p style="text-align: justify;"><code><em>}</em></code></p>
<p style="text-align: justify;"><code><em>ReactDOM.render(, document.getElementById('root'));</em></code></p>
<p style="text-align: justify;">&nbsp;</p>
<p style="text-align: justify;">&nbsp;</p>
<p style="text-align: justify;">&nbsp;</p>
<p style="text-align: justify;">In the above example, useEffect runs on every render. Whenever the count changes, a render happens and triggers another effect.</p>
<p style="text-align: justify;">But you wouldn&rsquo;t want this to happen. Including the second parameter can resolve the problems here.</p>
<p style="text-align: justify;"><strong>When no dependency is passed</strong></p>
<p style="text-align: justify;"><code>useEffect(() =&gt; {</code></p>
<p style="text-align: justify;"><code>&nbsp;&nbsp;//Runs on every render</code></p>
<p style="text-align: justify;"><code>});</code></p>
<p style="text-align: justify;"><strong>When there&rsquo;s an empty array</strong></p>
<p style="text-align: justify;"><code>useEffect(() =&gt; {</code></p>
<p style="text-align: justify;"><code>&nbsp;&nbsp;//Runs only on the first render</code></p>
<p style="text-align: justify;"><code>}, []);</code></p>
<p style="text-align: justify;"><strong>When props or state values are passed</strong></p>
<p style="text-align: justify;"><code>useEffect(() =&gt; {</code></p>
<p style="text-align: justify;"><code>&nbsp;&nbsp;//Runs on the first render</code></p>
<p style="text-align: justify;"><code>&nbsp;&nbsp;//And any time any dependency value changes</code></p>
<p style="text-align: justify;"><code>}, [prop, state]);</code></p>
<p style="text-align: justify;"><code>This issue can be fixed; you must run the effect only on the initial render.</code></p>
<p style="text-align: justify;"><code><em>import { useState, useEffect } from "react";</em></code></p>
<p style="text-align: justify;"><code><em>import ReactDOM from "react-dom";</em></code></p>
<p style="text-align: justify;"><code><em>function Timer() {</em></code></p>
<p style="text-align: justify;"><code><em>&nbsp;&nbsp;const [count, setCount] = useState(0);</em></code></p>
<p style="text-align: justify;"><code><em>&nbsp;&nbsp;useEffect(() =&gt; {</em></code></p>
<p style="text-align: justify;"><code><em>&nbsp;&nbsp;&nbsp;&nbsp;setTimeout(() =&gt; {</em></code></p>
<p style="text-align: justify;"><code><em>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;setCount((count) =&gt; count + 1);</em></code></p>
<p style="text-align: justify;"><code><em>&nbsp;&nbsp;&nbsp;&nbsp;}, 1000);</em></code></p>
<p style="text-align: justify;"><code><em>&nbsp;&nbsp;} []); // &lt;- add empty brackets here</em></code></p>
<p style="text-align: justify;"><code><em>&nbsp;&nbsp;return</em></code></p>
<p style="text-align: justify;">&nbsp;</p>
<h1>I've rendered {count} times!</h1>
<p style="text-align: justify;">&nbsp;</p>
<p style="text-align: justify;"><code><em>;</em></code></p>
<p style="text-align: justify;"><code><em>}</em></code></p>
<p style="text-align: justify;"><code><em>ReactDOM.render(, document.getElementById('root'));</em></code></p>
<p style="text-align: justify;">In the following example of useEffect Hook, the function is dependent on a variable. This means that the effect will run again when the count variable updates.</p>
<p style="text-align: justify;"><code><em>import { useState, useEffect } from "react";</em></code></p>
<p style="text-align: justify;"><code><em>import ReactDOM from "react-dom";</em></code></p>
<p style="text-align: justify;"><code><em>function Counter() {</em></code></p>
<p style="text-align: justify;"><code><em>&nbsp;&nbsp;const [count, setCount] = useState(0);</em></code></p>
<p style="text-align: justify;"><code><em>&nbsp;&nbsp;const [calculation, setCalculation] = useState(0);</em></code></p>
<p style="text-align: justify;"><code><em>&nbsp;&nbsp;useEffect(() =&gt; {</em></code></p>
<p style="text-align: justify;"><code><em>&nbsp;&nbsp;&nbsp;&nbsp;setCalculation(() =&gt; count * 2);</em></code></p>
<p style="text-align: justify;"><code><em>&nbsp;&nbsp;}, [count]); // &lt;- add the count variable here</em></code></p>
<p style="text-align: justify;"><code><em>&nbsp;&nbsp;return (</em></code></p>
<p style="text-align: justify;"><code><em>&nbsp;&nbsp;&nbsp;&nbsp;&lt;&gt;</em></code></p>
<p><code>Count: {count}</code></p>
<p style="text-align: justify;"><code><em>&nbsp;<button>setCount((c)=&gt; c+1)}&gt;+</button><button spellcheck="false" data-lt-tmp-id="lt-698263" data-gramm="false"></button></em></code></p>
<p><code>Calculation: {calculation}</code></p>
<p style="text-align: justify;"><code><em>&nbsp;&nbsp;&nbsp;&nbsp;&lt;/&gt;</em></code></p>
<p style="text-align: justify;"><code><em>&nbsp;&nbsp;);</em></code></p>
<p style="text-align: justify;"><code><em>}</em></code></p>
<p style="text-align: justify;"><code><em>ReactDOM.render(, document.getElementById('root'));</em></code></p>
<p style="text-align: justify;"><strong>Effects with Cleanup</strong></p>
<p style="text-align: justify;">Some effects in React require cleanup. For example, when effects like timeouts and subscriptions are no longer needed, they should be disposed of.</p>
<p style="text-align: justify;">Adding a return function towards the end will do this job. In the following example, the timer is cleaned up at the end of the useEffect Hook.</p>
<p style="text-align: justify;"><code><em>import { useState, useEffect } from "react";</em></code></p>
<p style="text-align: justify;"><code><em>import ReactDOM from "react-dom";</em></code></p>
<p style="text-align: justify;"><code><em>function Timer() {</em></code></p>
<p style="text-align: justify;"><code><em>&nbsp;&nbsp;const [count, setCount] = useState(0);</em></code></p>
<p style="text-align: justify;"><code><em>&nbsp;&nbsp;useEffect(() =&gt; {</em></code></p>
<p style="text-align: justify;"><code><em>&nbsp;&nbsp;&nbsp;&nbsp;let timer = setTimeout(() =&gt; {</em></code></p>
<p style="text-align: justify;"><code><em>&nbsp;&nbsp;&nbsp;&nbsp;setCount((count) =&gt; count + 1);</em></code></p>
<p style="text-align: justify;"><code><em>&nbsp;&nbsp;}, 1000);</em></code></p>
<p style="text-align: justify;"><code><em>&nbsp;&nbsp;return () =&gt; clearTimeout(timer)</em></code></p>
<p style="text-align: justify;"><code><em>&nbsp;&nbsp;}, []);</em></code></p>
<p style="text-align: justify;"><code><em>&nbsp;&nbsp;return</em></code></p>
<p style="text-align: justify;">&nbsp;</p>
<h1>I've rendered {count} times!</h1>
<p style="text-align: justify;">&nbsp;</p>
<p style="text-align: justify;"><code><em>;</em></code></p>
<p style="text-align: justify;"><code><em>}</em></code></p>
<p style="text-align: justify;"><code><em>ReactDOM.render(, document.getElementById("root"));</em></code></p>
<p>&nbsp;</p>

<p>To call a function on each re-render</p>

<p>To call a function a first render only</p>

<p>To call a function when any specific state changes.</p>

<p>What does empty dependency list ( <strong>[ ]</strong> ) mean?</p>

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