This example demonstrates a mouse-tracking visualization using React, where a circle follows the cursor’s position across an SVG canvas. The app initializes the circle at the center of a 960×500 viewport and updates its coordinates on every `mousemove` event. It uses React hooks (`useState` and `useCallback`) to manage and memoize the mouse position state. The rendering relies on ReactDOM and SVG elements, with no external data source, purely illustrating interactive event handling and declarative updates.