let xspeed = 3;

function setup() {

  createCanvas(400, 400);

}

​

function draw() {

  background(220);

  //x++;

  //ball is always moving

  x += xspeed; 

  if (x > width) xspeed *= -1;

  //if (x>width || x< 0) zspeed *= -1

  else if (x<0) xspeed *= -1;

  ellipse(x,height/2,20,20);

}