​

let width = 500;

let height = 300;

r = 20; // radius of the ball

​

// initial position of ball

x = 100;

y = 100;

speed = 0; // default speed

// direction of motion

dx = speed;

dy = speed;

​

function setup() {

  const canvas = createCanvas(width, height);

}

​

function draw() {

  background(240);

​

  x += dx;

  y += dy;

​

  if ((x > width-r) || (x < r)) {

    dx = dx * -1;

  }

  if ((y > height-r) || (y < r)) {

    dy = dy * -1;

  }

​

  fill('blue');

  circle(x, y, r*2);

}

​