React.js is one of the most popular and widely used libraries for building user interfaces, particularly single-page applications (SPAs). Developed by Facebook, React allows developers to create complex and dynamic web applications using a component-based architecture. Whether you’re a beginner in web development or transitioning from another framework, React offers an approachable yet powerful toolset for creating modern, interactive UIs.
In this step-by-step guide, we’ll walk you through the process of building your first React application. By the end of this guide, you’ll have a fully functional React app running on your local machine, and you’ll be familiar with the key concepts and features of React.
Prerequisites
Before we start, make sure you have the following tools installed:
- Node.js and npm: React relies on Node.js to run and npm (Node Package Manager) to manage project dependencies.
- Download Node.js from the official website.
- Code Editor: A good code editor, such as Visual Studio Code (VS Code), is essential for working with React.
- Download Visual Studio Code from here.
Once these tools are installed, you’re ready to get started!
Step 1: Setting Up Your React Development Environment
To create a React application, you’ll need to use Create React App, a tool developed by Facebook that sets up a new React project with sensible defaults.
Installing Create React App
- Open your terminal or command prompt.
Install Create React App globally by running the following command:
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npm install -g create-react-app
Creating a New React App
Once Create React App is installed, you can generate a new project:
- In your terminal, navigate to the directory where you want to create your app.
Run the following command to create a new React app (replace my-first-react-app with your desired project name):
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create-react-app my-first-react-app
This command will create a new folder with all the necessary files and configurations to start working with React. After it completes, you can move into your project directory:
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cd my-first-react-app
Step 2: Running the Development Server
Now that the project is set up, you can run the development server to see your React app in action:
In your terminal, run the following command to start the development server:
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npm start
- This will open your default web browser and navigate to http://localhost:3000. You should see the default React app running, with a welcome message and the React logo.
At this point, you’ve successfully set up your first React application, and you can start modifying it!
Step 3: Understanding the Project Structure
The project structure generated by Create React App looks like this:
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my-first-react-app/
├── node_modules/ # Project dependencies
├── public/ # Static files (index.html, etc.)
├── src/ # Application code (JSX, components, etc.)
│ ├── App.css # App styles
│ ├── App.js # Main App component
│ ├── index.css # Global styles
│ ├── index.js # Entry point for React app
├── package.json # Project metadata and dependencies
└── README.md # Project documentation
Key Files:
- public/index.html: The HTML file where your React components will be rendered. React attaches the app to the div with the id root.
- src/index.js: The JavaScript entry point. This is where React is initialized and the root component (usually App) is rendered.
- src/App.js: The main component where you’ll start building your application.
Step 4: Modifying the App Component
Let’s start by modifying the default React component to display your own content.
- Open the src/App.js file.
Replace the existing content with the following code:
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import React from ‘react’;
import ‘./App.css’;
function App() {
return (
<div className=”App”>
<h1>Welcome to My First React App!</h1>
<p>This is a simple React app built from scratch.</p>
</div>
);
}
export default App;
- Save the file. The browser should automatically refresh and show your changes.
Here’s what we’ve done:
- We defined a functional component called App using the function keyword.
- The JSX inside the return statement is rendered on the screen. JSX allows us to write HTML-like code in JavaScript.
- We used a CSS file (App.css) for styling, which is imported at the top of the file.
Step 5: Understanding JSX and React Components
What is JSX?
JSX stands for JavaScript XML. It is a syntax extension for JavaScript that allows you to write HTML-like code inside JavaScript. JSX makes it easier to describe the UI in React because it combines the power of JavaScript and HTML.
In the App component, we returned JSX that looks similar to HTML:
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return (
<div className=”App”>
<h1>Welcome to My First React App!</h1>
<p>This is a simple React app built from scratch.</p>
</div>
);
Although it looks like HTML, it is actually JavaScript. React converts this JSX into actual DOM elements when the component renders.
React Components
React apps are made up of components, which are self-contained, reusable pieces of code that define how a part of the UI should appear.
In the previous step, App was a component. React components can be either functional components (like the App component) or class components (although class components are less common in modern React development, they are still widely used).
Functional components are simpler and easier to write, and they’re the recommended choice for most new React code.
Step 6: Adding State to Your App
React is all about building interactive UIs. To make your app dynamic, you need to add state to your components.
Let’s update the App component to include state that tracks the number of button clicks.
First, import the useState hook from React at the top of your file:
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import React, { useState } from ‘react’;
Then, modify the App component to include state and a button that updates it:
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import React, { useState } from ‘react’;
import ‘./App.css’;
function App() {
// Declare a state variable
const [count, setCount] = useState(0);
// Function to handle button click
const handleClick = () => {
setCount(count + 1);
};
return (
<div className=”App”>
<h1>Welcome to My First React App!</h1>
<p>Button clicked {count} times</p>
<button onClick={handleClick}>Click Me!</button>
</div>
);
}
export default App;
- Save the file and check the app in the browser.
What’s Happening Here?
- We imported the useState hook from React. The useState hook is used to declare state variables in functional components.
- The count variable holds the number of times the button has been clicked, and setCount is the function used to update count.
- The button element has an onClick event handler that updates the count state every time it is clicked.
Now, when you click the button, the count value will increase, and the page will automatically update to reflect the new state. This is React’s reactivity at work.
Step 7: Styling Your React App
Let’s add some basic styling to make the app look better.
Open src/App.css and add the following styles:
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.App {
text-align: center;
margin-top: 50px;
}
h1 {
color: #61dafb;
}
button {
background-color: #282c34;
color: white;
border: none;
padding: 10px 20px;
font-size: 16px;
cursor: pointer;
}
button:hover {
background-color: #61dafb;
}
- Save the CSS file, and your app should now have a styled heading and button.
Step 8: Building and Deploying Your App
Once you’ve completed your app and are ready to deploy, you can build the production-ready version of your app with the following command:
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npm run build
This will create a build folder with optimized and minified production code. You can deploy this build folder to a static site hosting service like Netlify, Vercel, or GitHub Pages.
Conclusion
Congratulations! You’ve just built your first React application. In this guide, we covered the basic steps of setting up React, creating components, using state, and styling your app. You now have the foundation to explore more advanced React concepts like routing, forms, and data fetching.
React is an incredibly powerful library, and as you continue to develop your skills, you’ll be able to build more complex and dynamic applications.