let circleY = 100;

let xSpeed = 3;

let diameter = 50;

​

function setup() {

  createCanvas(400, 400);

}

​

function draw() {

  background(220);

  fill("red");

  noStroke();

  circle(circleX, circleY, diameter);

  circleX = circleX + xSpeed;

  let radius = diameter / 2;

  if((circleX - radius) < 0 || (circleX + radius) > width){

    xSpeed = xSpeed * -1;

  }

}

​

​

​

​

​

​

​

​

​