How React JS Works Internally? ?????

React JS is a popular JavaScript library for building user interfaces, particularly single-page applications. Understanding how React JS works internally helps developers create more efficient and effective applications. This article delves into the internals of React JS, covering its architecture, rendering process, reconciliation, hooks, and Fiber architecture, among other key aspects.

1. Introduction

React JS, developed by Facebook, has become a cornerstone in modern web development. Its declarative style, component-based structure, and efficient rendering make it a preferred choice for developers. To fully grasp how React JS operates, it's essential to understand its underlying mechanisms. This knowledge not only aids in building better applications but also in debugging and optimizing existing ones.

2. React Architecture

React's architecture is built around components and the Virtual DOM. These core concepts enable React to manage UI updates efficiently and maintain high performance.

Components

Components are the building blocks of a React application. They can be either functional or class-based. Each component encapsulates its own logic and UI, making it reusable and easy to manage. Components can be nested, allowing for complex UIs to be broken down into manageable pieces.

Functional Components

Functional components are simple JavaScript functions that return JSX. They are stateless by default but can hold state using hooks introduced in React 16.8.

function Greeting(props) {

  return <h1>Hello, {props.name}</h1>;

}        

?Class Components

Class components are ES6 classes that extend React.Component. They have more features, such as lifecycle methods and state management, compared to functional components.

class Greeting extends React.Component {

  render() {

    return <h1>Hello, {this.props.name}</h1>;

  }

}        

Virtual DOM

The Virtual DOM is a lightweight representation of the actual DOM. React maintains a Virtual DOM to optimize rendering. When the state of a component changes, React updates the Virtual DOM first. It then compares this updated Virtual DOM with the previous version to identify what has changed. This process is known as diffing.

The Virtual DOM improves performance by minimizing direct DOM manipulations, which are inherently slow. By updating only the parts of the DOM that have changed, React ensures that applications remain responsive and fast.

3. Rendering Process

The rendering process in React involves converting the Virtual DOM into the actual DOM. Here’s a step-by-step breakdown:

Initial Render

When a React application starts, React creates the Virtual DOM tree based on the initial state of the components. This Virtual DOM is a JavaScript object that represents the structure of the UI.

Reconciliation

React compares the current Virtual DOM with the previous one to find the differences. This process is known as reconciliation. React uses an efficient diffing algorithm to perform this comparison quickly.

Commit Phase

Once the differences are identified, React updates the actual DOM based on these changes. This phase is known as the commit phase. React batches updates and applies them in a single transaction to improve performance.

Example

Consider a simple example where a button click updates a counter:

function Counter() {

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

 

  return (

    <div>

      <p>{count}</p>

      <button onClick={() => setCount(count + 1)}>Increment</button>

    </div>

  );

}        

When the button is clicked, React updates the Virtual DOM first. It then compares the new Virtual DOM with the previous one, identifies the changes, and updates the actual DOM accordingly.

4. Reconciliation

Reconciliation is the process through which React updates the DOM. It involves two main steps: diffing and patching.

Diffing

React uses an algorithm to compare the new Virtual DOM tree with the previous one. This algorithm identifies the changes (additions, deletions, and updates) in a time-efficient manner. The key to React's performance is its ability to quickly determine what has changed in the UI and update only those parts.

Patching

Once the differences are identified, React updates the actual DOM. This process is optimized to minimize the number of updates and improve performance. By applying changes in batches, React ensures that the DOM is updated efficiently.

Key Algorithm

React's diffing algorithm is designed to handle updates efficiently. It operates on the assumption that components with the same key are similar, allowing React to reuse elements and avoid unnecessary re-renders. This key-based diffing is crucial for lists and dynamic content.

5. Hooks

Hooks are a recent addition to React that allows developers to use state and other React features in functional components. The most commonly used hooks are useState and useEffect.

useState

The useState hook allows you to add state to functional components. It returns a state variable and a function to update that state. This hook is essential for managing local state in functional components.

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

In this example, count is the state variable, and setCount is the function to update the state.

useEffect

The useEffect hook allows you to perform side effects in functional components. It replaces the lifecycle methods in class components. This hook runs after the render phase, making it suitable for tasks like data fetching, subscriptions, or manually changing the DOM.

useEffect(() => {

  // Code to run on component mount

}, []);        

Custom Hooks

Custom hooks are a way to extract reusable logic from components. They are JavaScript functions that use other hooks. Custom hooks help in organizing and reusing stateful logic across multiple components.

function useWindowWidth() {

  const [width, setWidth] = useState(window.innerWidth);

 

  useEffect(() => {

    const handleResize = () => setWidth(window.innerWidth);

    window.addEventListener('resize', handleResize);

 

    return () => {

      window.removeEventListener('resize', handleResize);

    };

  }, []);

 

  return width;

}        

6. Fiber Architecture

React's Fiber architecture is a complete rewrite of the React core algorithm. It aims to improve the rendering performance by allowing incremental rendering. This means React can split rendering work into chunks and spread it out over multiple frames.

Incremental Rendering

Incremental rendering allows React to pause work and come back to it later. This improves the responsiveness of the application, especially for complex updates. Fiber introduces a scheduling algorithm that prioritizes updates based on their urgency. For instance, user interactions are given higher priority over background data fetching.

Scheduling

Fiber's scheduling algorithm enables React to break down rendering work into units of work. Each unit of work can be paused and resumed, making it possible to handle high-priority updates promptly. This ensures that the user experience remains smooth even when the application is performing complex tasks.

Phases of Fiber

Fiber operates in two main phases: the render phase and the commit phase.

Render Phase: During this phase, Fiber builds a work-in-progress tree that represents the changes needed. This tree is created incrementally, allowing React to pause and resume work as needed.

Commit Phase: Once the render phase is complete, the commit phase begins. During this phase, React updates the actual DOM and applies the changes. This phase is optimized to be as fast as possible to ensure a smooth user experience.

Fiber Nodes

In the Fiber architecture, each element in the React tree corresponds to a Fiber node. These nodes hold information about the component, its state, and its effects. The Fiber nodes are linked to form a tree structure, which React traverses during the rendering process.

Benefits of Fiber

Fiber brings several benefits to React:

Improved performance: By breaking down rendering work into smaller units, Fiber improves the performance of React applications, especially during complex updates.

Better prioritization: Fiber's scheduling algorithm allows React to prioritize updates based on their urgency, ensuring that user interactions remain smooth.

Enhanced debugging: Fiber provides more detailed information about the rendering process, making it easier to debug and optimize React applications.

Conclusion

Understanding how React JS works internally provides valuable insights into its performance optimizations and rendering efficiency. By leveraging components, the Virtual DOM, reconciliation, hooks, and the Fiber architecture, React ensures that applications remain fast and responsive.

React's architecture and internal workings are designed to handle the complexities of modern web development, making it a powerful tool for developers. Whether you're building simple interfaces or complex single-page applications, React's robust internals ensure a smooth development experience.

React's continual evolution, with features like hooks and the Fiber architecture, demonstrates its commitment to performance and developer experience. As a developer, understanding these internals not only enhances your ability to build efficient applications but also equips you with the knowledge to troubleshoot and optimize existing ones.

In summary, React JS's internal workings—comprising components, the Virtual DOM, reconciliation, hooks, and the Fiber architecture—form the backbone of its efficiency and popularity. This understanding is crucial for any developer looking to master React and build high-performance web applications. For businesses seeking top-rated React JS web development services, understanding these internals ensures better collaboration with developers and more effective project outcomes.

Shiv Technolabs, a leading React JS development company, offers unparalleled expertise in building dynamic and responsive web applications. When you hire React JS developers?from Shiv Technolabs, you benefit from a team well-versed in the intricacies of React's architecture, ensuring your projects are handled with the highest level of proficiency and care.