​

var on = false

​

function setup() {

  createCanvas(400, 400);

}

​

function draw() {

  background(0);

​

  if (on) {

    background(255);

  } else {

    background(0);

  }

​

  rectMode(CENTER);

  stroke(0);

  fill(255);

  rect(200, 200, 100, 100);

​

}

​

function mousePressed() {

  if (mouseX > 150 && mouseX < 250 && mouseY > 150 && mouseY < 250) {

    on = !on

  }

}