​

function setup() {

  canvas = createCanvas(400, 400);

  pg = createGraphics(400, 400);

}

​

function draw() {

  background(220, 0, 0);

  pg.circle(mouseX, mouseY, 100);

  image(pg, 0, 0);

}

​

function keyPressed() {

  if(key === 's' || key === 'a') {

    const link = document.createElement('a');

    link.download = 'canvas.png';

    if(key === 's')

      link.href = pg.elt.toDataURL();

    else

      link.href = canvas.elt.toDataURL();

    link.click();

    link.remove();

  }

}

​