createCanvas(600, 600);

}

​

function draw() {

  background(0);

  stroke(255);

  strokeWeight(4);

  background(0);

  // at each x coordinate...

  for (let x = 100; x <= 500; x += 50) {

    // make an entire column of circles

    for (let y = 100;  y <= 500; y += 50) {

      ellipse(x, y, 50, 50);

    }

  }

}