How does the virtual DOM work in React?


The React Virtual DOM is a crucial concept that enhances the performance of React applications by efficiently updating the actual DOM (Document Object Model) when the state of the application changes. It acts as an abstraction layer between the application’s logic and the browser’s rendering engine. Here’s how it works:

  1. Initial Render: When you create a React component and render it to the DOM, React generates a virtual representation of the component’s structure, also known as the Virtual DOM. This Virtual DOM is a lightweight copy of the actual DOM and contains elements and their properties.

  2. State and Props Changes: When the state or props of a component change due to user interactions or other events, React re-renders the component and generates a new Virtual DOM representation.

  3. Reconciliation: React then performs a process called “reconciliation” to compare the new Virtual DOM with the previous one. It efficiently identifies the differences (diffing) between the two representations.

  4. Generating Updates: Based on the differences detected during reconciliation, React creates a minimal set of updates that need to be applied to the actual DOM to reflect the changes. This set of updates is optimized for performance.

  5. Batching Updates: React batches multiple updates together to minimize the number of actual DOM manipulations. This batching reduces the performance overhead associated with interacting with the DOM.

  6. Updating the Actual DOM: Once React has the set of updates ready, it applies them to the actual DOM using a process known as “reconciliation” or “diffing” algorithm. Only the parts of the DOM that need to be changed are modified, which results in efficient updates and improved performance.

  7. Efficiency Gains: The Virtual DOM allows React to avoid unnecessary direct manipulation of the actual DOM for every state change. By performing updates in memory first and then optimizing the application of changes to the actual DOM, React minimizes the browser’s reflow and repaint operations, leading to a smoother user experience.

  8. Optimizations: React also implements various optimization techniques, such as using keys to uniquely identify elements in collections, to enhance the efficiency of the reconciliation process and minimize unnecessary updates.

In summary, the React Virtual DOM works by maintaining a lightweight copy of the actual DOM in memory. When there are changes in the application’s state or props, React calculates the minimal updates required to sync the Virtual DOM with the actual DOM. This process reduces the performance overhead associated with direct manipulation of the DOM, leading to faster and more efficient rendering in React applications.

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