This example shows a single circle that follows the mouse cursor across an SVG canvas. The circle’s position is updated live based on pointer movement, with its center coordinates directly mapped from the browser’s clientX and clientY events. Built with React and D3 v5, the code uses React’s useState and useCallback hooks to manage the mouse position state, while rendering the circle as a SVG <circle> element. The interaction demonstrates a simple, responsive data-binding pattern between user input and a visual element.