function setup() {

  createCanvas(1000, 500);

    button = createButton('square');

  button.position(510, 270);

  button.mousePressed(draw);

  button.size (100)

}

​

function draw() {

  if (mouseIsPressed) {

  rect (500, 250, random(300), random(350))

  fill (random(255), random (255), random (255))

}

}