createCanvas(windowWidth, windowHeight);

}

​

let xPos = 0;

let xVel = 4;

​

function draw() {

  background(220, 20, 120);

  ellipse(xPos, height / 2, 50);

  xPos = xPos + xVel;

  if (xPos > width) {

    xVel = -4;

  } else if (xPos < 0) {

    xVel = 4;

  }

}

​