createCanvas(400, 400);

}

​

let x=0;

let speedx=10;

function draw() {

  background(0);

  noFill()

  stroke(255)

  circle(x,height/2,100)

  x=x+speedx

  if (x>width) {

    //speedx=-10

    speedx*=-1

  }

  if (x<0) {

    //speedx=10

    speedx*=-1

  }

}