​

function setup() {

  createCanvas(400, 400);

  for (let b = 0; b < 20; b++) {

    balls.push(

      new Ball(random(width), random(height), random(-5, 5), random(-1, 1))

    );

  }

}

​

function draw() {

  background(220);

  for (let ball of balls) {

    ball.move();

    ball.bounce();

    ball.display();

  }

}

​

// Define Ball (capitalized because it's a class)

class Ball {

  constructor(x, y, xspeed, yspeed) {

    //'this' refers to the ball object 

    this.x = x;

    this.y = y;

    this.xspeed = xspeed;

    this.yspeed = yspeed;

  }

​

  move() {

    this.x += this.xspeed;

    this.y += this.yspeed;

  }

​

  bounce() {

    if (this.x < 0 || this.x > width) {

      this.xspeed *= -1;

    }

    if (this.y < 0 || this.y > height) {  // Change from 'width' to 'height'

      this.yspeed *= -1;

    }

  }

​

  display() {

    ellipse(this.x, this.y, 50, 50);

  }

}

​