React Course: How React Apps Work

React is a JavaScript library developed by Facebook, optimized for building user interfaces. It is primarily used for developing single-page applications (SPAs) and allows for efficient work with reusable UI components. In this course, I will explain in detail how React apps work.

1. What is React?

React is a component-based library designed to simplify the construction of complex applications. The core idea of React is to create “components,” small abstract entities that make up the UI.

2. Basic Concepts of React

2.1. Components

Components are independent pieces that make up the UI as part of React. Each component can have its own state and properties, allowing them to perform various actions.

2.2. State and Props

React builds dynamic UIs through a component’s “state” and “props.” The state is managed within the component and changes according to user interactions. In contrast, props are the data passed from a parent component to a child component.

3. Structure of a React App

A React application consists of multiple components. Each component can contain other components, enabling the construction of complex UIs. Typically, a single root component encompasses all child components.

3.1. Example Structure


/App
  ├─ /Header
  ├─ /Main
  │   ├─ /Sidebar
  │   └─ /Content
  └─ /Footer

4. How React Apps Work

4.1. DOM and Virtual DOM

One of the most significant features of React is the concept of “Virtual DOM.” React uses Virtual DOM to optimize performance rather than directly accessing the real DOM. The Virtual DOM is a virtual representation of the DOM structure in memory, comparing differences with the actual DOM to minimize updates.

4.2. Process of Operation

  1. When a React component is rendered, a Virtual DOM is created.
  2. When the state changes, a new Virtual DOM is generated.
  3. Previous and new Virtual DOMs are compared (diffing).
  4. Only the changed parts are updated in the real DOM.

4.3. Example Code


import React, { useState } from 'react';

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

    const increment = () => {
        setCount(count + 1);
    };

    return (
        

            
Current Count: {count}

            
        

    );
}

5. State Management

State management is an essential part of React applications. For complex state management, tools like Redux and MobX can be utilized.

5.1. State Management Using Redux

Redux is a pattern that centrally manages the entire state of the application. All states are stored in a store, and components are connected to this store to exchange data.

5.2. Example Code


import { createStore } from 'redux';

// Initial state
const initialState = {
    count: 0
};

// Define reducer
const reducer = (state = initialState, action) => {
    switch (action.type) {
        case 'INCREMENT':
            return { ...state, count: state.count + 1 };
        default:
            return state;
    }
};

// Create store
const store = createStore(reducer);

6. Deploying React Applications

React applications are transformed into static files through a build process and can be deployed on a web server. Generally, create-react-app can be used for easy setup for deployment.

6.1. Deployment Method

  1. Build with the command npm run build.
  2. Upload the resulting /build directory to the web server.

7. Conclusion

React is a powerful and flexible UI library that allows for easy management of complex applications through component-based programming. The use of Virtual DOM significantly enhances the performance of DOM updates, and state management libraries enable more systematic state management. Explore new possibilities in web application development with React.

8. References