A smiley face icon follows the user's cursor across an SVG canvas, updating its position in real time as the mouse moves. Built with React and D3 v5, the example uses React's `useState` and `useCallback` hooks to track mouse coordinates and trigger re-renders. The `onMouseMove` handler on the SVG element captures client coordinates, which are then passed to a circle element's `cx` and `cy` attributes to reposition the face.