ellipse_rect_switch.js

var y = 0;
var isEllipse = true;

function setup() {
  createCanvas(600, 400);
  rectMode(CENTER);
}

function draw() {
  background(0);

  if (isEllipse == true) {
    ellipse(width / 2, y, 50, 50);
  } else {
    rect(width / 2, y, 50, 50);
  }

  if (y > height) {
    isEllipse = false;
  }
  if (y < 0) {
    isEllipse = true;
  }
}

function keyPressed() {
  if (keyCode == DOWN_ARROW) {
    y += 10;
  } else if (keyCode == UP_ARROW) {
    y -= 10;
  }

}