ReactJS — Virtual DOM

ReactJS uses a Virtual DOM (Document Object Model) to efficiently update the user interface (UI) of web applications. The Virtual DOM is an abstraction of the actual DOM, a representation of the document’s structure and content in memory. Here’s how the Virtual DOM works in React:

1. Real DOM vs. Virtual DOM:

• The Real DOM is the actual structure of the web page, and any changes to it can be time-consuming and inefficient.
• The Virtual DOM is a lightweight copy of the Real DOM, maintained by React. It is a JavaScript representation of the UI.

2. Component Rendering:

• In React, UIs are built using components. Each component has a render method that describes what the UI should look like at any given point in time.
• When a component’s state or props change, React re-renders the component, creating a new Virtual DOM representation.

3. Reconciliation:

• React compares the new Virtual DOM with a snapshot of the previous one.
• It calculates the minimal number of changes needed to update the Real DOM.

4. Diffing Algorithm:

• React uses a reconciliation algorithm (often referred to as the “diffing algorithm”) to efficiently identify the differences between the new and old Virtual DOM.
• It minimizes the number of updates by only updating the parts of the Real DOM that have changed.

5. Batching Updates:

• React batches multiple updates into a single update to minimize the number of trips to the Real DOM.
• This batching process is asynchronous, and updates are typically handled within a single “tick” of the JavaScript event loop.

6. Updating the Real DOM:

• Once the minimal set of changes is determined, React updates the Real DOM with these changes.
• This process is faster than directly manipulating the entire Real DOM because it only involves the specific elements that have changed.

7. Performance Benefits:

• The Virtual DOM helps in improving performance by reducing the amount of direct manipulation of the Real DOM, which can be slow.
• The diffing algorithm ensures that only necessary updates are made to the Real DOM, minimizing the overall computational cost.

In summary, React’s Virtual DOM is a key optimization technique for updating the UI efficiently, providing a smoother user experience in web applications.