How does Virtual DOM works in React js?

Virtual DOM (Document Object Model) is a concept used in frameworks like React.js to optimize the performance of web applications by minimizing unnecessary updates to the actual DOM.

Here's how Virtual DOM works:

1. Initial Render: When you write code in a framework like React.js, you create components with JSX (JavaScript XML) syntax. When your application starts, React creates a virtual representation of the DOM in memory, which is essentially a lightweight copy of the actual DOM.

2. Updating State: When the state of your application changes (due to user interactions, data fetching, etc.), React re-renders the affected components. Instead of directly updating the actual DOM, React updates the virtual DOM.

3. Reconciliation: After the virtual DOM has been updated, React performs a process called reconciliation. React compares the new virtual DOM with the previous one to determine the minimal set of changes needed to update the actual DOM.

4. Diffing Algorithm: React uses a reconciliation algorithm to efficiently compute the differences between the new virtual DOM and the previous one. It identifies which parts of the virtual DOM have changed and calculates the most efficient way to update the actual DOM.

5. Batching Updates: React batches multiple updates together and performs them in a single DOM update operation. This helps improve performance by reducing the number of times the actual DOM is accessed and modified.

6. Updating the DOM: Once React has determined the necessary changes to the actual DOM, it updates the DOM accordingly. However, it only updates the parts of the DOM that have changed, rather than re-rendering the entire DOM tree.

By using a Virtual DOM, React is able to minimize the amount of work needed to update the actual DOM, resulting in improved performance and a smoother user experience. Additionally, the Virtual DOM abstracts away the complexities of directly manipulating the DOM, making it easier to write and maintain complex web applications.

Diagram illustrating how Virtual DOM works:

                    +-------------------------+
                    |       Virtual DOM       |
                    +-------------------------+
                             /      \
                            /        \
                           /          \
                          /            \
            +----------------+       +-----------------+
            |   Component    |      |    Component     |
            |   State: A     |      |   State: B       |
            +----------------+      +-----------------+
                   |                         |
                   |                         |
                   |   Update State          |   Update State
                   |   (setState)            |   (setState)
                   |                         |
            +----------------+        +-----------------+
            |  Virtual DOM   |        |  Virtual DOM    |
            |  State: A'     |        |   State: B'     |
            +----------------+        +-----------------+
                   |                         |
                   |                         |
                   |  Reconciliation         |
                   |  (Diffing Algorithm)    |
                   |                         |
                   +-----------+-------------+
                               |
                   +-----------v-------------+
                   |     Actual DOM          |
                   |   Updated Accordingly   |
                   +-------------------------+

In this diagram:

• Components have their own state (State: A, State: B) represented within each component block.
• When a component's state changes (Update State), React updates the corresponding Virtual DOM.
• After updates to the Virtual DOM, React performs reconciliation (Diffing Algorithm) to determine the minimal set of changes needed to update the Actual DOM.
• Finally, React updates the Actual DOM based on the changes identified during reconciliation.