<canvas id="canvas"></canvas>

const canvas = document.getElementById("canvas");
const ctx = canvas.getContext("2d");

canvas.width = window.innerWidth * devicePixelRatio;
canvas.height = window.innerHeight * devicePixelRatio;

const canvasW = canvas.width;
const canvasH = canvas.height;

let hue = 0;
function colorful() {
  hue += 0.5;
  if (hue > 360) {
    hue = 0;
  }
  ctx.beginPath();
  ctx.arc(200,200, 200, 0, Math.PI * 2);
  ctx.fillStyle = `hsl(${hue},100%,50%)`;
  ctx.fill();
  requestAnimationFrame(colorful);
}
colorful();