let vel;

​

function setup() {

  createCanvas(400, 400);

  loc = createVector(width/2, height/2);

  vel = createVector(2.0, 3.0);

}

​

function draw() {

  background(220);

  if (loc.x > width || loc.x < 0) {

    vel.x *= -1;

  }

  if (loc.y > height || loc.y < 0) {

    vel.y *= -1;

  }

  ellipse(loc.x, loc.y, 15, 15)

  loc.add(vel)

}