How the React engine works under the hood, and how React applies hooks

Learn how the React engine works under the hood and how React applies hooks to manage state and lifecycle in functional components. Discover the power of React's virtual DOM and reconciliation algorithm. Explore the built-in hooks like useState and useEffect for state management and performing side effects. Stay updated with the latest features and best practices in React to build robust and scalable applications.

Introduction

React is a popular JavaScript library for building user interfaces.

It has gained immense popularity due to its simplicity and efficiency.

In this blog post, we will explore how the React engine works under the hood and how React applies hooks to manage state and lifecycle in functional components.

The React Engine

The React engine is responsible for rendering components, managing state, and handling updates efficiently.

It uses a virtual DOM (Document Object Model) to optimize the rendering process.

When a component's state changes, React updates the virtual DOM and compares it with the real DOM to determine the minimal set of changes needed to update the UI.

React uses a reconciliation algorithm called "diffing" to efficiently update the DOM.

It compares the previous and current virtual DOM trees and applies only the necessary changes to the real DOM.

This approach minimizes the number of DOM manipulations, resulting in better performance.

React Components

In React, components are the building blocks of the user interface.

They can be either class components or functional components. Class components are defined using ES6 classes and have lifecycle methods, while functional components are defined as functions and do not have lifecycle methods.

Functional components are simpler and easier to understand. They are also more performant because they don't have the overhead of lifecycle methods.

However, functional components lacked state management until the introduction of hooks in React 16.8.

React Hooks

React hooks are a feature introduced in React 16.8 that allows functional components to manage state and lifecycle.

They provide a way to reuse stateful logic without writing a class component.

Hooks are functions that "hook into" React's internal state management and lifecycle features.

There are several built-in hooks provided by React, such as useState, useEffect, useContext, and more.

These hooks can be used to manage state, perform side effects, and access context within functional components.

useState Hook

The useState hook allows functional components to have state. It takes an initial state value and returns an array with two elements:

The current state value and a function to update the state. Here's an example:

import React, { useState } from 'react';

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

  return (
    
      Count: {count}
      
    
  );
}

In the above example, the useState hook is used to manage the count state.

The count value is displayed in the UI, and the setCount function is used to update the count when the button is clicked.

useEffect Hook

The useEffect hook allows functional components to perform side effects, such as fetching data, subscribing to events, or updating the DOM. It takes a function as its first argument and runs it after every render. Here's an example:

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

function DataFetcher() {
  const [data, setData] = useState(null);

  useEffect(() => {
    fetchData().then((response) => setData(response));
  }, []);

  return (
    
      {data ? Data: {data}
 : Loading...}
    
  );
}

In the above example, the useEffect hook is used to fetch data and update the state.

The fetchData function is called after the component is rendered for the first time, indicated by the empty dependency array [] as the second argument. This ensures that the effect runs only once.

Conclusion

React's engine and the introduction of hooks have revolutionized the way we build user interfaces in JavaScript.

The virtual DOM and the reconciliation algorithm make React efficient and performant.

Hooks provide a simpler and more intuitive way to manage state and lifecycle in functional components.

By understanding how the React engine works under the hood and how React applies hooks, developers can leverage the power of React to build robust and scalable applications.