How to Build a Bidirectional Radar Chart with Draggable Vertices Using React

A developer has documented a React-based pattern for building an interactive SVG radar chart where vertices can be dragged directly, with changes instantly reflected in linked sliders and vice versa. The key insight is avoiding dual state management: instead of syncing two separate states, both the chart and sliders share a single source of truth via one state store and one update function. Coordinate math converts slider values (0–100) to polar coordinates, placing each axis vertex at equal angular intervals around a central point. Dragging a vertex triggers the same update function used by the sliders, eliminating the need for any explicit synchronization logic. The article, originally published in Japanese on forge.workstyle.tech, covers pointer event handling, coordinate transformation, and how the design scales across charts with varying numbers of axes.