Fork of Smiley Face Part III
This example shows a simple smiley face composed of a yellow circle, two eyes, and a smiling mouth, all centered in an SVG canvas. It demonstrates how to integrate React with D3 by using D3’s `arc()` generator to create the mouth path and rendering it as a React `<path>` element. The code relies on React 16.9 and D3 v5, using JSX to define SVG shapes with numeric constants for positioning and sizing. The face is drawn declaratively, with all geometry derived from fixed values like `eyeOffsetX`, `mouthRadius`, and `strokeWidth`.