This example demonstrates interactive mouse tracking in an SVG visualization built with React and D3 v7. A single circle follows the cursor’s position across an 800×500 pixel canvas, with its coordinates updated dynamically through React’s `useState` and `useCallback` hooks. The `onMouseMove` event handler captures client X and Y values, while ReactDOM renders the SVG element and its circle child. The visualization shows how React manages stateful rendering for real-time geometric updates, with the imported D3 library available but unused in the current logic.