let speedY = 7;

let x = 0;

let y = 0;

​

function setup() {

  createCanvas(400, 400);

}

​

function draw() {

  background(0);

  stroke(255);

  strokeWeight(4);

  noFill();

  ellipse(x,y,20,20);

  if((x>width)||(x<0)){

    speedX *= -1;

  }

  if((y>height)||(y<0)){

    speedY *= -1;

  }

  x = x + speedX;

  y = y + speedY;

​

​

}

​