function setup() {

  createCanvas(720, 400);

  background(51);

  noStroke();

  noLoop();

}

​

function draw() {

  drawTarget(width * 0.25, height * 0.4, 200, 4);

  drawTarget(width * 0.5, height * 0.5, 300, 10);

  drawTarget(width * 0.75, height * 0.3, 120, 6);

}

​

function drawTarget(xloc, yloc, size, num) {

  const grayvalues = 255 / num;

  const steps = size / num;

  for (let i = 0; i < num; i++) {

    fill(i * grayvalues);

    ellipse(xloc, yloc, size - i * steps, size - i * steps);

  }

}

​