Q1. What is the Virtual DOM in React?
The Virtual DOM is a lightweight JavaScript representation of the actual DOM. It is an in-memory tree of React elements that React uses to optimize updates. When state changes, React creates a new virtual DOM tree and compares it with the previous one to find the minimal changes needed, then updates the real DOM efficiently.
Q2. How does the Virtual DOM improve performance?
Direct manipulation of the real DOM is slow. The Virtual DOM allows React to batch multiple changes and update the real DOM in a single operation. By using diffing algorithms, React updates only the changed parts instead of re-rendering the whole page, leading to faster and smoother UI updates.
Q3. Explain the process of reconciliation in React.
Reconciliation is the process by which React updates the DOM. When a component's state or props change, React creates a new virtual DOM tree. It then diffs this new tree with the previous one using a heuristic algorithm (based on key and element type). After identifying the differences, React updates only those parts in the real DOM.
Q4. What is the role of keys in the Virtual DOM?
Keys help React identify which items in a list have changed, been added, or removed. They give elements a stable identity, enabling React to optimize re-rendering by reusing DOM nodes. Keys should be unique among siblings and stable (avoid using array indexes if the list can change).
Q5. Does the Virtual DOM replace the real DOM?
No, the Virtual DOM is an abstraction on top of the real DOM. React uses it to compute the most efficient way to update the real DOM. The real DOM is still the ultimate source of truth for what is displayed, but React minimizes direct manipulations to improve performance.