let y;

let speedX = 3;

let speedY = 5;

let d = 50;

​

​

function setup() {

  createCanvas(400, 400);  

  x = random(0, width);

  y = random(0, height);

  speedX = random(-10, 10);

  speedY = random(-10, 10);

}

​

function draw() {

  background(220);

  circle(x, y, d);

​

  x = x + speedX;

  y = y + speedY;

  if (x > width - d/2 || x < d/2) {

    speedX = -speedX;

  }

  if (y > height - d/2 || y < d/2) {

    speedY = -speedY; 

  } 

}