let y;

let d; // direction

let c; // colour

​

function setup() {

  createCanvas(400, 400);

  x = 30

  y = 200

  d = +5

  c = +255

}

​

function draw() {

  background(220, 0 ,0);

  noStroke()

  circle(x, y, 60);

  if (x > 29 && x < width-30) {

    fill(c);

    d = d

  }

  else {

   d = -d

  } 

   x = x+d

}