This example shows a smiley face drawn with SVG primitives in D3.js v5, featuring a randomly colored face, fixed eyes, and a curved mouth. It demonstrates fundamental DOM manipulation by appending circles and a path directly to an SVG container. A button triggers a color change, using `transition().duration(500).attr('fill', ...)` to animate the face’s fill to a new random HSL value generated by `getRandomColor()`. The code relies on D3’s selection and transition APIs without any external data source.