text: // define variable for ball count paragraph
  
  const para = document.querySelector('p');
  let count = 0;
  
  // setup canvas
  
  const canvas = document.querySelector('canvas');
  const ctx = canvas.getContext('2d');
  
  const width = canvas.width = window.innerWidth;
  const height = canvas.height = window.innerHeight;
  
  // function to generate random number
  
  function random(min,max) {
    const num = Math.floor(Math.random()*(max-min)) + min;
    return num;
  }
  
  // define shape constructor
  
  function Shape(x, y, velX, velY, exists) {
    this.x = x;
    this.y = y;
    this.velX = velX;
    this.velY = velY;
    this.exists = exists;
  }
  
  // define Ball constructor, inheriting from Shape
  
  function Ball(x, y, velX, velY, exists, color, size) {
    Shape.call(this, x, y, velX, velY, exists);
  
    this.color = color;
    this.size = size;
  }
  
  Ball.prototype = Object.create(Shape.prototype);
  Ball.prototype.constructor = Ball;
  
  // define ball draw method
  
  Ball.prototype.draw = function() {
    ctx.beginPath();
    ctx.fillStyle = this.color;
    ctx.arc(this.x, this.y, this.size, 0, 2 * Math.PI);
    ctx.fill();
  };
  
  // define ball update method
  
  Ball.prototype.update = function() {
  
    // What to do when balls hit wall
    if((this.x + this.size) >= width) {
      this.velX = -(this.velX);
    }
  
    if((this.x - this.size) <= 0) {
      this.velX = -(this.velX);
    }
  
    if((this.y + this.size) >= height) {
      this.velY = -(this.velY);
    }
  
    if((this.y - this.size) <= 0) {
      this.velY = -(this.velY);
    }
  // Moving animation
    this.x += this.velX;
    this.y += this.velY;
  };
  
  // define ball collision detection
  
  Ball.prototype.collisionDetect = function() {
    for(var j = 0; j < balls.length; j++) {
      if(!(this === balls[j])) {
        var dx = this.x - balls[j].x;
        var dy = this.y - balls[j].y;
        var distance = Math.sqrt(dx * dx + dy * dy);
  
        if (distance < this.size + balls[j].size && balls[j].exists) {
          balls[j].color = this.color = 'rgb(' + random(0,255) + ',' + random(0,255) + ',' + random(0,255) +')';
        }
      }
    }
  };
  
  // define EvilCircle constructor, inheriting from Shape
  
  function EvilCircle(x, y, exists) {
    Shape.call(this, x, y, 20, 20, exists);
  
    this.color = 'white';
    this.size = 10;
  }
  
  EvilCircle.prototype = Object.create(Shape.prototype);
  EvilCircle.prototype.constructor = EvilCircle;
  
  
  // define EvilCircle draw method
  
  EvilCircle.prototype.draw = function() {
    ctx.beginPath();
    ctx.strokeStyle = this.color;
    ctx.lineWidth = 3;
    ctx.arc(this.x, this.y, this.size, 0, 2 * Math.PI);
    ctx.stroke();
  };
  
  
  // define EvilCircle checkBounds method
  
  EvilCircle.prototype.checkBounds = function() {
    if((this.x + this.size) >= width) {
      this.x -= this.size;
    }
  
    if((this.x - this.size) <= 0) {
      this.x += this.size;
    }
  
    if((this.y + this.size) >= height) {
      this.y -= this.size;
    }
  
    if((this.y - this.size) <= 0) {
      this.y += this.size;
    }
  };
  
  // define EvilCircle setControls method
  
  EvilCircle.prototype.setControls = function() {
    var _this = this;
    window.onkeydown = function(e) {
      if(e.key === 'a') {
        _this.x -= _this.velX;
      } else if(e.key === 'd') {
        _this.x += _this.velX;
      } else if(e.key === 'w') {
        _this.y -= _this.velY;
      } else if(e.key === 's') {
        _this.y += _this.velY;
      }
    };
  };
  
  // define EvilCircle collision detection
  
  EvilCircle.prototype.collisionDetect = function() {
    for(let j = 0; j < balls.length; j++) {
      if( balls[j].exists ) {
        const dx = this.x - balls[j].x;
        const dy = this.y - balls[j].y;
        const distance = Math.sqrt(dx * dx + dy * dy);
  
        if (distance < this.size + balls[j].size) {
          balls[j].exists = false;
          count--;
          para.textContent = 'Ball count: ' + count;
        }
      }
    }
  };
  
  
  
  // define array to store balls and populate it
  
  const balls = [];
  
  while(balls.length < 25) {
    const size = random(10,20);
    let ball = new Ball(
      // ball position always drawn at least one ball width
      // away from the adge of the canvas, to avoid drawing errors
      random(0 + size,width - size),
      random(0 + size,height - size),
      random(-7,7),
      random(-7,7),
      true,
      'rgb(' + random(0,255) + ',' + random(0,255) + ',' + random(0,255) +')',
      size
    );
    balls.push(ball);
    count++;
    para.textContent = 'Ball count: ' + count;
  }
  
  // define loop that keeps drawing the scene constantly
  
  let evil = new EvilCircle(random(0,width), random(0,height), true);
  evil.setControls();
  
  function loop() {
    ctx.fillStyle = 'rgba(0,0,0,0.25)';
    ctx.fillRect(0,0,width,height);
  
    for(let i = 0; i < balls.length; i++) {
      if(balls[i].exists) {
        balls[i].draw();
        balls[i].update();
        balls[i].collisionDetect();
      }
    }
  
    evil.draw();
    evil.checkBounds();
    evil.collisionDetect();
  
    requestAnimationFrame(loop);
  }
  
  
  
  loop();
  
  
  
  