let hSpeed = 2;

let circleY = 200;

let vSpeed = 3;

let circleHue = 0;

​

​

function setup() {

  createCanvas(400, 400);

  colorMode(HSB);

  background(0);

  noStroke();

}

​

function draw() {

  fill(circleHue, 100, 100);

  circleHue = circleHue + 5;

  if(circleHue >= 360) {

    circleHue = 0;

  }

  ellipse(circleX, circleY, 50);

  circleX = circleX + hSpeed;

  //  If the circle is at the right OR left edge

  if (circleX >= 375 || circleX <= 25) {

    //  Switch the direction

    hSpeed = -hSpeed;

  }

  circleY = circleY + vSpeed;

  //  If the circle is at the top OR bottom edge

  if (circleY >= 375 || circleY <= 25) {

    vSpeed = -vSpeed;

  }

}