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How Does ReactJS Work? A Comprehensive Guide

Madhav Gajjar

Dec 14, 2023

5 min readLast Updated Jan 03, 2024

React JS has gained widespread popularity and become a dominant force in web development, empowering developers to create interactive, scalable, and high-performance web applications. With its component-based architecture, declarative programming paradigm, and robust ecosystem of tools and libraries, React has become the preferred choice for building modern web applications.

React JS, an open-source JavaScript library for building user interfaces (UIs), is maintained by Facebook and a community of individual developers and companies. It utilizes a component-based approach, dividing UIs into small, reusable pieces called components. This modularity makes React applications easier to develop, maintain, and scale.

Significance of React JS in Modern Web Development

React JS has gained immense popularity among web developers due to its numerous advantages, including:

  • Component-based architecture: React's component-based approach promotes code reusability and maintainability, making it easier to manage complex web applications.

  • Declarative programming: React encourages developers to describe the desired UI state, rather than explicitly manipulating the DOM, leading to more concise and predictable code.

  • Virtual DOM: React utilizes a virtual DOM, an in-memory representation of the real DOM, to efficiently update the UI without re-rendering the entire page.

  • Large ecosystem of tools and libraries: React boasts a rich ecosystem of tools and libraries, such as Redux, React Router, and Axios, that enhance its capabilities and simplify development tasks.

How Does React JS Work?

ReactJS, a popular JavaScript library for building user interfaces, works through a series of interconnected mechanisms. Let's explore each step in detail, with examples and numbers for better understanding.

1. Understanding the Component-Based Architecture

  • React's core concept revolves around components, self-contained units representing UI elements with their own logic and rendering code.
  • Components can be nested within each other, building complex UIs with modularity and reusability.
  • Consider a simple blog post component. It could be composed of other components like header, title, content, and author section, each with its own responsibility.

2. Properties (props) and State

  • Components receive data from their parents through properties, also called props.
  • Props are immutable, meaning they cannot be modified within the receiving component. They act as an input to the component's rendering.
  • Each component also maintains its own state, an object containing its internal data that dictates its behavior and rendering.
  • For example, a "Like Button" component might have a state variable called "isLiked" that determines whether the button displays "Like" or "Unlike".

3. The Virtual DOM

  • React uses a virtual DOM, an in-memory representation of the real DOM (Document Object Model), the tree structure of HTML elements displayed on the screen.
  • This virtual DOM is lightweight and allows React to perform efficient updates.
  • When a component's state or props change, React creates a new virtual DOM tree and compares it to the previous one.
  • Only the parts of the real DOM that have changed are updated, minimizing unnecessary manipulations and improving performance.

4. Initial Rendering and Data Flow

  • When a React application loads, it renders the initial components based on their initial state and props.
  • Data flows in a single direction, from parent components to child components through props.
  • This ensures predictable behavior and simplifies state management.

5. Reconciliation and Efficient Updates

  • Any user interaction or data update triggers a re-render of the affected components.
  • React then performs a reconciliation process, comparing the new virtual DOM tree to the previous one.
  • Only the necessary parts of the real DOM are updated, reflecting the changes in the virtual DOM.
  • This minimizes DOM manipulation and optimizes performance, especially for complex UIs.

6. Component Lifecycle

  • Each React component has a lifecycle consisting of different phases:
  • Mounting: When the component is first created and inserted into the DOM.
  • Updating: When the component receives new props or state changes.
  • Unmounting: When the component is removed from the DOM.
  • Developers can utilize lifecycle methods to perform specific actions at each stage, such as fetching data during mounting or cleaning up side effects during unmounting.

7. Extending React with the Ecosystem

  • React's rich ecosystem offers numerous libraries and tools that enhance its functionality:
  • Redux: A state management library for managing complex application states across components.
  • React Router: A routing library for handling navigation within a single-page application.
  • Axios: A library for making HTTP requests, simplifying data fetching from APIs.

8. Building and Bundling with React

  • To run in browsers, React applications need to be bundled into JavaScript files.
  • Webpack is a popular bundler that combines React components, JavaScript code, and other resources into a single file.
  • Transpilers like Babel convert JSX, a syntax extension for writing UI elements in JavaScript, into plain JavaScript that browsers can understand.

Real-world Examples

React JS is used by a wide range of companies and organizations to build their web applications. Here are a few notable examples:

  • Facebook: React JS is the foundation of Facebook's web infrastructure, powering its dynamic and interactive user interface.

  • Instagram: Instagram utilizes React JS to create its visually appealing and engaging user experience.

  • Netflix: Netflix employs React JS to deliver its streaming service's user interface across various devices.

  • Airbnb: Airbnb relies on React JS to build its interactive and user-friendly accommodation booking platform.

  • Uber: Uber utilizes React JS to power its mobile and web applications for ride-sharing services.

React JS is constantly evolving, with new features and trends emerging. Here are a few key directions to watch:

  • Server-side rendering: React is increasingly being used for server-side rendering, optimizing initial page load performance.

  • Functional programming: Functional programming concepts are gaining traction in React development, leading to more concise and maintainable code.

  • GraphQL: GraphQL is becoming a popular choice for data fetching in React applications, offering more flexibility and control over data retrieval.

  • Progressive Web Apps (PWAs): React is well-suited for building PWAs, providing a native-like user experience.

Getting Started with React JS Now

You can start building your applications with a solid understanding of React JS fundamentals. Numerous resources, including tutorials, documentation, and online communities, can guide you through the process.

We, at Third Rock Techkno, offer dedicated development solutions for ensuring a high-quality market-driven product development that can cater to your business goals efficiently. Check out our portfolio and drop us a line to get started today!


1. How does React work behind the scenes?

React utilizes a virtual DOM, a representation of the real DOM, to efficiently update the UI. It compares the virtual DOM to the actual DOM and updates only the necessary parts, optimizing performance.

2. Is React a front-end or back-end?

React is a front-end library used to build the user interface of web applications. It interacts with back-end services through APIs to fetch and manipulate data.

3. Which is harder: React or JavaScript?

React builds upon JavaScript, adding a component-based architecture and declarative programming paradigm.

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