How to Build a React JS App from Scratch: A Comprehensive Guide

In today’s digital age, web development has become an essential skill for individuals and businesses alike. Among the various frameworks available, React JS stands out as one of the most popular choices due to its flexibility, performance, and ease of use. If you’re interested in building a React JS app from scratch but don’t know where to start, you’ve come to the right place. In this comprehensive guide, we’ll take you through the step-by-step process of building your own React JS app, covering everything from setup to deployment.

Getting Started with React JS

What is React JS?

React JS is a JavaScript library developed by Facebook that allows you to build user interfaces for web applications. It follows a component-based architecture, where each component represents a reusable piece of UI. React JS efficiently updates and renders components when the underlying data changes, making it highly performant.

Setting Up Your Development Environment

Before diving into React JS development, you’ll need to set up your development environment. Here are the steps to get started:

1. Install Node.js: Visit the official Node.js website (https://nodejs.org) and download the LTS version suitable for your operating system. Follow the installation instructions to complete the setup.
2. Choose a Code Editor: You can use any code editor of your choice, such as Visual Studio Code, Atom, or Sublime Text. Install your preferred code editor and ensure it’s up to date.

Creating a New React JS Project

Once your development environment is set up, you can create a new React JS project using Create React App. This tool allows you to quickly scaffold a React project with all the necessary configurations. Follow these steps:

1. Open your terminal or command prompt.
2. Navigate to the directory where you want to create your project.
3. Run the following command to create a new React project:
4. npx create-react-app my-app
5. Replace “my-app” with the desired name for your project.
6. Wait for the project to be created. Once finished, navigate into the project folder:
7. cd my-app

Understanding the React Component Structure

In React JS, components are the building blocks of your application’s user interface. Components can be divided into two types: functional components and class components.

Functional components are simple JavaScript functions that return JSX (a syntax extension for JavaScript). They are easier to write and understand compared to class components.

Class components, on the other hand, are JavaScript classes that extend the React.Component class. They allow you to implement additional features such as state and lifecycle methods.

Customizing Your Project

Once you have created your React project, you can start customizing it to fit your needs. Here are some common customizations you might want to consider:

• Project Structure: Review the project structure and organize your files and folders based on your application’s architecture.
• Styling: Choose a styling approach for your project, such as CSS modules, CSS-in-JS libraries, or inline styles.
• Adding Libraries: Install and import additional libraries you need for your project, such as UI frameworks or data fetching libraries.
• Configuring ESLint: Customize ESLint rules to enforce code quality and maintain consistency across your project.
• Setting Up Git: Initialize a Git repository for version control and set up a remote repository if necessary.
• Adding Tests: Implement unit tests or component tests to ensure the stability and reliability of your application.

By customizing your project, you can tailor it to meet the specific requirements of your React JS app.

Building Your First React Component

Creating a Functional Component

To build a React component, you can start by creating a functional component. Functional components are simpler and recommended for simple UI elements that don’t require state or lifecycle methods.

In your project, create a new file called MyComponent.js and add the following code:

import React from 'react';

function MyComponent() {
  return (
    <div>
      <h1>Hello, World!</h1>
      <p>This is my first functional component.</p>
    </div>
  );
}

export default MyComponent;

In the code above, we import React and define a function called MyComponent that returns JSX. JSX allows us to write HTML-like code within JavaScript. The component renders a <div> element containing an <h1> heading and a <p> paragraph.

Adding JSX and Rendering Components

To render a component in your app, you need to add JSX code to the root component. By default, the root component is located in the src/index.js file. Open that file and modify it as follows:

import React from 'react';
import ReactDOM from 'react-dom';
import MyComponent from './MyComponent';

ReactDOM.render(
  <React.StrictMode>
    <MyComponent />
  </React.StrictMode>,
  document.getElementById('root')
);

In the code above, we import ReactDOM and our MyComponent. Then, we use the ReactDOM.render() method to render the MyComponent component. The rendered component is inserted into the HTML element with the root id.

Working with Props

Props allow you to pass data from a parent component to a child component. This enables you to reuse components and customize their behavior. Let’s modify our MyComponent to accept and display a prop:

import React from 'react';

function MyComponent(props) {
  return (
    <div>
      <h1>Hello, {props.name}!</h1>
      <p>This is my first functional component.</p>
    </div>
  );
}

export default MyComponent;

In the code above, we added props as a parameter to the MyComponent function. We can now access the name prop using props.name.

To pass the name prop, modify the ReactDOM.render() call in src/index.js as follows:

ReactDOM.render(
  <React.StrictMode>
    <MyComponent name="John" />
  </React.StrictMode>,
  document.getElementById('root')
);

In this example, we pass the name prop with the value “John” to the MyComponent component. The component will render “Hello, John!”.

State and Lifecycle Methods

Class components in React JS allow you to manage state and use lifecycle methods. State represents the data that can change over time, affecting the component’s behavior and rendering.

Let’s create a class component called Counter that increments a counter value every second:

import React from 'react';

class Counter extends React.Component {
  constructor(props) {
    super(props);
    this.state = {
      count: 0
    };
  }

  componentDidMount() {
    this.interval = setInterval(() => {
      this.setState((prevState) => ({
        count: prevState.count + 1
      }));
    }, 1000);
  }

  componentWillUnmount() {
    clearInterval(this.interval);
  }

  render() {
    return (
      <div>
        <h1>Counter: {this.state.count}</h1>
      </div>
    );
  }
}

export default Counter;

In the code above, we define the Counter class component that extends React.Component. The component has a count state initialized to 0 in the constructor. We use the componentDidMount() lifecycle method to start an interval that increments the count every second using this.setState(). The componentWillUnmount() method is used to clean up the interval when the component is unmounted.

To render the Counter component, modify the ReactDOM.render() call in src/index.js as follows:

ReactDOM.render(
  <React.StrictMode>
    <Counter />
  </React.StrictMode>,
  document.getElementById('root')
);

Now, when you run the app, you’ll see the counter value increasing every second.

Handling Events

React JS allows you to handle events, such as button clicks or form submissions, using event handlers. Let’s create a simple form with a button that updates the component’s state:

import React from 'react';

class Form extends React.Component {
  constructor(props) {
    super(props);
    this.state = {
      name: ''
    };
  }

  handleChange(event) {
    this.setState({
      name: event.target.value
    });
  }

  handleSubmit(event) {
    event.preventDefault();
    alert('Hello, ' + this.state.name + '!');
  }

  render() {
    return (
      <form onSubmit={(e) => this.handleSubmit(e)}>
        <label>
          Name:
          <input type="text" value={this.state.name} onChange={(e) => this.handleChange(e)} />
        </label>
        <button type="submit">Submit</button>
      </form>
    );
  }
}

export default Form;

In the code above, we define the Form class component with a name state. The handleChange() method updates the state as the user types in the input field. The handleSubmit() method is called when the form is submitted, displaying an alert with the entered name.

To render the Form component, modify the ReactDOM.render() call in src/index.js as follows:

ReactDOM.render(
  <React.StrictMode>
    <Form />
  </React.StrictMode>,
  document.getElementById('root')
);

Now, when you run the app, you can enter your name in the form and click the Submit button to see the alert.

Managing State with React

Understanding State in React

In React JS, state is a JavaScript object that represents the mutable data within a component. State allows components to manage and update their data dynamically, leading to a more interactive user experience.

To use state in a functional component, you can leverage React’s useState hook. Let’s modify our Counter component from earlier to use state with the useState hook:

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

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

  useEffect(() => {
    const interval = setInterval(() => {
      setCount((prevCount) => prevCount + 1);
    }, 1000);

    return () => clearInterval(interval);
  }, []);

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

export default Counter;

In the code above, we import useState and useEffect from React. We use the useState hook to declare a count state variable and a setCount function to update the state. In the useEffect hook, we set up an interval to increment the count every second and return a cleanup function to clear the interval.

Handling Events with State

State in React allows you to handle events and update the component’s data accordingly. Let’s create a simple form component that handles input changes and displays the entered text:

import React, { useState } from 'react';

function Form() {
  const [name, setName] = useState('');

  const handleChange = (event) => {
    setName(event.target.value);
  };

  return (
    <form>
      <label>
        Name:
        <input type="text" value={name} onChange={handleChange} />
      </label>
      <p>Hello, {name}!</p>
    </form>
  );
}

export default Form;

In the code above, we use the useState hook to create a name state variable and a setName function to update it. The handleChange function is called when the input value changes, updating the name state. The entered name is then displayed using JSX.

Context API for Global State Management

In larger applications, passing props down through multiple layers of components can become cumbersome. React’s Context API provides a solution for sharing data across the component tree without explicit prop drilling.

To demonstrate the Context API, let’s create a theme-switching app that allows the user to toggle between light and dark themes. First, we’ll create the context:

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

export const ThemeContext = createContext();

export const ThemeProvider = ({ children }) => {
  const [theme, setTheme] = useState('light');

  const toggleTheme = () => {
    setTheme((prevTheme) => (prevTheme === 'light' ? 'dark' : 'light'));
  };

  return (
    <ThemeContext.Provider value={{ theme, toggleTheme }}>
      {children}
    </ThemeContext.Provider>
  );
};

In the code above, we create a ThemeContext using createContext() and provide a default value. We also create a ThemeProvider component that wraps its children with the ThemeContext.Provider. The provider component holds the theme state and the toggleTheme function for updating it.

Next, let’s create two components that consume the theme context:

import React, { useContext } from 'react';
import { ThemeContext } from './ThemeContext';

const ThemeToggler = () => {
  const { theme, toggleTheme } = useContext(ThemeContext);

  return (
    <button onClick={toggleTheme}>
      Switch to {theme === 'light' ? 'dark' : 'light'} theme
    </button>
  );
};

const ThemeDisplay = () => {
  const { theme } = useContext(ThemeContext);

  return <p>Current theme: {theme}</p>;
};

export { ThemeToggler, ThemeDisplay };

In the code above, we import useContext from React and the ThemeContext we created earlier. The ThemeToggler component uses useContext to access the theme state and the toggleTheme function from the context. It renders a button that toggles the theme when clicked. The ThemeDisplay component only displays the current theme.

Finally, let’s use the components within our app:

import React from 'react';
import { ThemeProvider } from './ThemeContext';
import { ThemeToggler, ThemeDisplay } from './ThemeComponents';

function App() {
  return (
    <ThemeProvider>
      <ThemeToggler />
      <ThemeDisplay />
    </ThemeProvider>
  );
}

export default App;

In this example, we wrap our components with the ThemeProvider so that the ThemeContext is available to them. We then render the ThemeToggler and ThemeDisplay components within the ThemeProvider.

Now, when the user clicks the theme toggler button, the theme will be updated and reflected in the ThemeDisplay component.

FAQs

Conclusion

In this article, we explored the process of building a React JS app from scratch. We covered the basics of React components, JSX, rendering, props, state, lifecycle methods, event handling, and managing global state using the Context API. By following the steps and examples provided, you should now have a solid understanding of how to start building your own React JS app and expand its functionality using various React features.

Remember to always refer to the React JS documentation and explore additional resources to deepen your knowledge and stay up to date with the latest advancements in React development. Happy coding!