What is reconciliation process?

The reconciliation process in React is the mechanism by which React determines which parts of the virtual DOM need to be updated based on changes in state or props, and efficiently applies those updates to the actual DOM. Reconciliation is a key part of React's declarative programming model, where you specify how your UI should look based on the current application state, and React takes care of updating the DOM to reflect those changes.

Here's an overview of how the reconciliation process works:

1. Render Phase: Whenever the state or props of a component change, React re-renders the component and its children in a virtual representation of the DOM called the "virtual DOM."

2. Differential Algorithm: React employs a "diffing" or "reconciliation" algorithm to compare the virtual DOM generated during the current render phase with the virtual DOM generated during the previous render phase. This process involves comparing each element of the virtual DOM tree and determining if any changes need to be applied to the actual DOM.

3. Keyed Elements: React uses keys assigned to each element in a collection (e.g., in lists or arrays of components) to efficiently identify which elements have been added, removed, or re-ordered since the last render. Keys help React determine the identity of elements across renders, ensuring that it can update the DOM efficiently without unnecessary re-renders or re-renders of unchanged elements.

4. Minimal Updates: React aims to minimize the number of updates required to bring the actual DOM into sync with the virtual DOM. Instead of re-rendering the entire component tree on each update, React selectively updates only the parts of the DOM that have changed. This approach improves performance by reducing the amount of work required to update the UI.

5. Component Lifecycle Methods: During the reconciliation process, React also invokes various component lifecycle methods, such as componentDidMount, componentDidUpdate, and componentWillUnmount, to allow components to perform side effects, update their internal state, or clean up resources as needed.

Overall, the reconciliation process in React plays a crucial role in ensuring that the UI remains in sync with the underlying application state while also optimizing performance by minimizing unnecessary updates to the DOM. By efficiently comparing virtual DOM trees and applying minimal updates to the actual DOM, React provides a fast and responsive user experience for web applications.