React 18 Core Packages

React is a JavaScript library for building user interfaces, designed with a focus on component-based architecture, declarative programming, and efficient update mechanisms.
At the core of React’s implementation, four key packages form the backbone of the framework: react-dom, react, react-reconciler, and scheduler.
This article delves into the design principles and implementation logic of these core packages to help developers new to React better understand the underlying concepts.

1. react-dom

react-dom is the package responsible for interacting with the browser’s DOM. Its primary role is to render React components into the actual DOM and efficiently update the DOM when the component’s state changes.

• createRoot: Introduced in React 18, this API creates a root container that supports concurrent features. It enables React to handle user interactions and animations more smoothly.
• render: This method renders React elements into the DOM. It leverages React’s reconciliation algorithm to calculate and apply only the necessary updates, ensuring optimal performance.

2. react

The react package is the core library of React, providing the foundational tools for creating components and managing state.

• useState: A Hook for managing state within functional components. It allows components to maintain internal state and triggers re-renders when the state changes.
• useEffect: A Hook for handling side effects, such as data fetching, subscriptions, or manual DOM manipulations. Its design separates side-effect logic from rendering logic, promoting cleaner and more maintainable code.

3. react-reconciler

react-reconciler is React’s reconciliation engine, responsible for computing changes in the component tree and generating an update plan. It is a core part of React that enables cross-platform rendering.

• createFiberRoot: Creates the root node of a Fiber tree. Fiber is the core data structure introduced in React 18 to support concurrent rendering.
• initializeUpdateQueue: Initializes the update queue, which stores state updates for components.
• enqueueUpdate: Adds new updates to the queue, awaiting processing by the reconciliation engine.

4. scheduler

scheduler is React’s task scheduler, managing the prioritization of tasks.
It ensures that high-priority tasks, such as user input, are handled first, while lower-priority tasks, like animations or data loading, can be deferred.

React’s scheduling mechanism is a cornerstone of its performance optimization. By using scheduler, React can efficiently update the UI without blocking the main thread, ensuring a responsive user experience.