function setup() {
  //starter image
  image = createImg("welcome.gif");
  image.class('gif');
  //remove and then show new gif
  button.mousePressed(removeGif);
  button.mouseReleased(showGif);
}

function showGif() {
  image = createImg(currentGif);
  image.class('gif');
}

function removeGif() {
  a = selectAll('.gif');
  for (let i = 0; i < a.length; i++) {
    a[i].remove();
  }
}