The Virtual DOM (VDOM) is a programming concept used to represent the user interface in memory. React uses its rendering and reconciliation process to determine which changes are required to make the actual browser DOM match the latest UI output.
When a component's state or props change, React renders the component again, compares the new result with the previous rendered result, and commits the necessary changes to the browser DOM. This allows developers to describe the desired UI instead of manually updating individual DOM elements.
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The Virtual DOM is an in-memory representation of a user interface that React uses during rendering. It describes the elements and components that should appear on the screen.
React uses this representation to determine how the UI has changed between renders. Instead of requiring developers to manipulate the browser DOM manually for every state change, React manages the necessary updates.
function App() {
return (
<div>
<h1>Welcome to React JS</h1>
<p>Learn the Virtual DOM.</p>
</div>
);
}
export default App;In this example, React elements describe a user interface containing a div, a heading, and a paragraph. React uses this description during rendering to determine what should appear in the browser.
The Real DOM, or Document Object Model, is the browser's representation of an HTML document. It represents page elements as nodes that JavaScript can access and manipulate.
<div id="root">
<h1>Welcome to React JS</h1>
<p>Learn the Virtual DOM.</p>
</div>The browser creates DOM nodes for the elements in the HTML document. JavaScript can update these nodes using DOM APIs.
const heading = document.getElementById("title");
heading.textContent = "Hello React!";This example directly changes the text of an existing DOM element. React applications usually update the UI through state and props rather than manually changing DOM elements that React manages.
| Virtual DOM | Real DOM |
|---|---|
| An in-memory representation used during React rendering. | The actual document tree maintained by the browser. |
| Helps React determine the required UI changes. | Displays and represents the page elements in the browser. |
| Works with React's rendering and reconciliation process. | Can be manipulated through browser DOM APIs. |
| Is not directly visible to the user. | Provides the elements that users see and interact with. |
| Describes the intended UI output. | Contains the actual HTML elements, attributes, and text nodes. |
| Changes are calculated as React renders. | Required changes are applied during React's commit phase. |
Modern web applications frequently change their interfaces in response to user actions, server data, and application state. Manually coordinating every DOM change can become complicated as an application grows.
React provides a declarative approach in which developers describe the UI based on the current data. React then manages rendering, reconciliation, and the required DOM updates.
React's rendering process can be understood through three main stages: triggering a render, rendering components, and committing changes to the DOM.
When an application starts, React renders its root component and determines the UI that should appear on the screen.
When relevant state or props change, React may render the affected component tree again to calculate the latest UI output.
React compares the new rendered output with the previous output to determine which parts of the UI need to change. This process is known as reconciliation.
React applies the necessary changes to the browser DOM. If an element's output has not changed, React may leave its corresponding DOM node untouched.
The browser paints the updated interface so that the user can see the changes.
User Interaction
|
v
State or Props Change
|
v
React Renders Components
|
v
New UI Representation
|
v
Reconciliation
|
v
Determine Necessary Changes
|
v
Commit Changes to Browser DOM
|
v
Browser Displays Updated UIReconciliation is the process React uses to determine how the rendered UI should change when a component produces new output.
React considers factors such as element types, their positions in the tree, and keys when deciding whether to update existing elements or replace them.
Suppose a component initially displays the following heading:
<h1>Welcome to React</h1>After a state update, it displays:
<h1>Welcome to Virtual DOM</h1>Because the element type remains h1, React can update the heading's text rather than replacing the entire page.
The following React component demonstrates how a state update changes the displayed text.
import { useState } from "react";
function App() {
const [message, setMessage] = useState("Hello World");
return (
<div>
<h1>{message}</h1>
<button onClick={() => setMessage("Hello React JS")}>
Change Message
</button>
</div>
);
}
export default App;The browser does not need to rebuild the entire document just to change this heading. React applies the necessary update through its rendering process.
| Direct DOM Manipulation | React Rendering |
|---|---|
| Developers manually select and modify DOM elements. | Developers update state or props and describe the desired UI. |
| Application code must coordinate DOM changes directly. | React manages rendering and commits required updates. |
| May become difficult to maintain when many UI elements depend on changing data. | Components and declarative rendering help organize UI behavior. |
| Uses browser APIs such as querySelector and textContent. | Typically uses JSX, components, state, and event handlers. |
Direct DOM manipulation is not inherently wrong. It is useful in many web development situations. However, developers should avoid manually changing DOM nodes that React owns unless they are using an appropriate integration pattern, such as refs.
React Fiber is the internal reconciliation architecture introduced in React 16. It organizes rendering work into units that React can schedule and process according to its rendering strategy.
Fiber is an implementation detail of React rather than a feature developers usually need to manage directly.
React's rendering approach is particularly useful for applications in which the UI changes frequently based on user interactions or changing data.
The Virtual DOM is a commonly used term for React's in-memory UI representation, which helps React determine the necessary updates to the browser DOM.
The Real DOM is the browser's actual document structure containing elements, attributes, and text nodes.
Reconciliation is the process React uses to determine the differences between previous and new rendered output.
No. React determines the required changes and commits the necessary DOM updates. A component can re-render without causing a DOM change.
The Virtual DOM is an in-memory UI representation used by libraries such as React. Shadow DOM is a browser feature that provides encapsulation for DOM structure and styling.
React Fiber is the internal reconciliation architecture that helps React organize and schedule rendering work.
No. React's rendering approach can help manage UI updates, but actual performance depends on the application and implementation.
Common causes include a component's state update, new props, or a context value change. A parent re-render can also cause child components to render again.
The commit phase is when React applies the necessary changes to the rendering environment, such as updating the browser DOM.
Keys help React identify list items across renders and determine how to update, preserve, or replace them.
The Virtual DOM is an important concept for understanding how React manages user-interface updates. React renders components to determine the desired UI, uses reconciliation to identify changes, and commits the necessary updates to the browser DOM.
Understanding rendering, reconciliation, state updates, component identity, and stable list keys helps developers build React applications that are easier to maintain and optimize.
