Understanding React Rendering: A Deep Dive
Understanding React Rendering: A Deep Dive

Understanding React Rendering: A Deep Dive

React, the popular open-source JavaScript library for building user interfaces, operates on a component-based architecture. To harness its power and create highly optimized and performant React apps, it’s crucial to comprehend how rendering works within React.

React Elements and Components

React Elements: The Building Blocks

React elements are the fundamental units in React applications. These plain JavaScript objects describe what appears on the screen. JSX (JavaScript XML) simplifies their creation, converting JSX syntax into React.createElement() function calls that yield JavaScript objects. Compared to browser DOM elements, React elements are less resource-intensive.

Key Element Properties
  • $$typeof: Identifies the object as a React element and enhances security.
  • key: Uniquely identifies elements among siblings when mapping over an array.
  • ref: References an actual DOM node or component instance.
  • props: Contains properties passed to the component.
  • type: Specifies the type of HTML element to create (string, React component, or fragment).
  • children: Defines the element’s content, accommodating multiple children.
React Components: Encapsulating Element Trees

React components encapsulate element trees and can be either classes or functions. Both types accept props as inputs and return an element tree as output. Functional components return the function’s value, while class components return the render method’s output. React manages components by creating instances, each possessing state and a lifecycle.

React’s Rendering Process

The Render Phase

Rendering in React involves describing the user interface based on the current state and props. The process comprises two phases: Render and Commit.

Initial Render

The initial render occurs when the application starts, beginning from the root component and building a React element tree representing the desired DOM structure.


Re-rendering, triggered by state changes, also constructs a new JavaScript representation of the DOM. It employs a process called diffing to identify differences between the old and new React element trees (virtual DOM).

The Virtual DOM

The virtual DOM consists of plain JavaScript objects that represent components and elements. React utilizes this virtual DOM to minimize costly updates to the actual DOM. When a component’s state changes, React compares the virtual DOM to determine which parts of the real DOM need updates.


Reconciliation bridges the rendering phases, synchronizing the virtual DOM with the real DOM. React avoids re-rendering the entire DOM by efficiently transforming one tree into another using the Diffing Algorithm. This heuristic O(n) algorithm ensures speedy updates by assuming that different element types produce distinct trees and using unique keys for frequently changing child elements.

The Commit Phase

The Commit Phase handles actual DOM manipulation. For the initial render, it uses the DOM API’s appendChild() to place newly created nodes on the screen. During re-renders, it applies minimal necessary operations calculated during rendering to align the DOM with the latest output.

React’s Interaction with the DOM

React interacts with the real DOM using third-party packages known as Renderers, such as React DOM for web platforms and React Native for mobile platforms. These Renderers manage actual DOM manipulation, while React provides a platform-agnostic means of defining components.

Tips for Render Performance Optimization

To optimize rendering in React, consider employing memoization techniques using hooks like useCallback() or useMemo(). Memoization caches component-rendered results, enhancing efficiency.

Additionally, keeping component state local where possible can prevent unnecessary re-renders, as state updates trigger re-renders in the owning component and its descendants.


Understanding React’s rendering process, element-component relationships, and optimization techniques is essential for building highly performant React applications. Mastery of these principles empowers developers to create efficient and responsive user interfaces in the React ecosystem.

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