How does React work? Tell me about Virtual DOM and the reconciliation mechanism.

React works based on the concept of Virtual DOM — a lightweight copy of the real DOM stored in memory. When the component's state changes, React first updates the Virtual DOM, then compares it with the previous version (a process called reconciliation).

The reconciliation mechanism allows for efficiently updating only the parts of the real DOM that have changed, instead of re-rendering the entire DOM. This significantly improves performance.

Main steps:

1. Changing the component's state triggers a re-render of the Virtual DOM.
2. React compares the new Virtual DOM with the previous one (diffing).
3. Calculates the minimal set of changes.
4. Applies these changes to the real DOM.

Thus, React provides a fast and optimal interface rendering.