let xpos = 20;

let ypos = 200;

let speed = 3;

​

function setup() {

  createCanvas(400, 400);

}

​

function draw() {

  background(220);

  ellipse(xpos, ypos, rad);

  if (xpos >= width-25) {

    speed = -3;

  }else if(xpos<10){

    speed=3;}

  xpos = xpos + speed;

}