createCanvas(400, 400);

  // if you move background() to setup() so that it is only

  // called once when you fist run the program then everything

  // you draw will permanently stay on the screen

  background(100, 0, 200);

}

​

function draw() {

  strokeWeight(10)

  stroke(0, 255, 0);

  fill(0, 0, 255);

  ellipse(mouseX, mouseY, 25, 25);

}