Phaser, ES2015 and Breakout

import Phaser from 'phaser';

class Game extends Phaser.Game {
  constructor (width, height, mode, domElement='content', arg=null) {
    super(width, height, mode, domElement, arg);
    this.state.add('Game', GameState, true);
  }
}

class GameState extends Phaser.State {
  constructor() {
    super();
    this.ball = null;
    this.paddle = null;
    this.bricks = null;
    this.brickInfo = null;
    this.score = 0;
    this.scoreText = null;
    this.lives = 3;
    this.livesText = null;
    this.lifeLostText = null;
    this.textStyle = {
      font: '18px Helvetica',
      fill: '#0095DD'
    };
    this.playing = false;
    this.startButton = null;
    this.ballHitPaddle = this.ballHitPaddle.bind(this);
    this.initBricks = this.initBricks.bind(this);
    this.ballHitBrick = this.ballHitBrick.bind(this);
    this.ballLeaveScreen = this.ballLeaveScreen.bind(this);
    this.startGame = this.startGame.bind(this);
  }

  preload() {
    this.scale.scaleMode = Phaser.ScaleManager.SHOW_ALL;
    this.scale.pageAlignHorizontally = true;
    this.scale.pageAlignVertically = true;
    this.stage.backgroundColor = '#eeeeee';
    this.load.image('ball', 'assets/sprites/ball.png');
    this.load.image('paddle', 'assets/sprites/paddle.png');
    this.load.image('brick', 'assets/sprites/brick.png');
    this.load.spritesheet('ball', 'assets/sprites/wobble.png', 20, 20);
    this.load.spritesheet('button', 'assets/sprites/button.png', 120, 40);
  }

  create() {
    this.physics.startSystem(Phaser.Physics.ARCADE);
    this.physics.arcade.checkCollision.down = false;

    this.ball = this.add.sprite(this.world.width * 0.5, this.world.height - 50,
      'ball');
    this.ball.animations.add('wobble', [0, 1, 0, 2, 0, 1, 0, 2, 0], 24);
    this.physics.enable(this.ball, Phaser.Physics.ARCADE);
    this.ball.body.collideWorldBounds = true;
    this.ball.checkWorldBounds = true;
    this.ball.events.onOutOfBounds.add(this.ballLeaveScreen, this);
    this.ball.body.bounce.set(1);

    this.paddle = this.add.sprite(this.world.width * 0.5,
      this.world.height - 10, 'paddle');
    this.paddle.scale.setTo(1.5, 1);
    this.paddle.anchor.setTo(0.5, 1);
    this.physics.enable(this.paddle, Phaser.Physics.ARCADE);
    this.paddle.body.collideWorldBounds = true;
    this.paddle.body.immovable = true;

    this.initBricks();
    this.bricks = game.add.group();
    // Add bricks
    for (let c = 0; c < this.brickInfo.count.col; c++) {
      for (let r = 0; r < this.brickInfo.count.row; r++) {
        let brickX = (r * (this.brickInfo.width + this.brickInfo.padding))
          + this.brickInfo.offset.left;
        let brickY = (c * (this.brickInfo.height + this.brickInfo.padding))
        + this.brickInfo.offset.top;
        let newBrick = this.add.sprite(brickX, brickY, 'brick');
        this.physics.enable(newBrick, Phaser.Physics.ARCADE);
        newBrick.body.immovable = true;
        newBrick.scale.setTo(2, 1.2);
        newBrick.anchor.set(0.5);
        this.bricks.add(newBrick);
      }
    }

    this.scoreText = this.add.text(5, 5, `Points: ${this.score}`, this.textStyle);

    this.livesText = this.add.text(this.game.world.width - 5, 5,
      `Lives: ${this.lives}`, this.textStyle);
    this.livesText.anchor.set(1,0);
    this.lifeLostText = this.add.text(this.world.width * 0.5,
      this.world.height * 0.5, 'Life lost, click to continue', this.textStyle);
    this.lifeLostText.anchor.set(0.5);
    this.lifeLostText.visible = false;

    this.startButton = this.add.button(this.world.width * 0.5,
      this.world.height * 0.5, 'button', this.startGame, this, 1, 0, 2);
    this.startButton.anchor.set(0.5);
  }

  update() {
    this.physics.arcade.collide(this.ball, this.paddle, this.ballHitPaddle);
    this.physics.arcade.collide(this.ball, this.bricks, this.ballHitBrick);
    if (this.playing) {
      this.paddle.x = this.input.x || (this.world.width * 0.5);
    }
  }

  initBricks() {
    this.brickInfo = {
      width: 100,
      height: 30,
      count: {
        row: 9,
        col: 5
      },
      offset: {
        top: 100,
        left: 200
      },
      padding: 10
    };
  }

  ballHitPaddle(ball, paddle) {
    ball.animations.play('wobble');
    ball.body.velocity.x = -1 * 5 * (paddle.x - ball.x);
  }

  ballHitBrick(ball, brick) {
    let killTween = this.add.tween(brick.scale);
    killTween.to({x: 0, y: 0}, 200, Phaser.Easing.Linear.None);
    killTween.onComplete.addOnce(() => {
      brick.kill();
    }, this);
    killTween.start();
    this.score += 10;
    this.scoreText.setText(`Points: ${this.score}`);

    let countAlive = this.bricks.filter((brick) => {
      return brick.alive;
    }).length;

    if (countAlive === 0) {
      alert('You\'ve won the game, congrats!');
    }
  }

  ballLeaveScreen() {
    this.lives -= 1;
    if (this.lives) {
      this.livesText.setText(`Lives: ${this.lives}`);
      this.lifeLostText.visible = true;
      this.ball.reset(this.world.width * 0.5, this.world.height - 50);
      this.paddle.reset(this.world.width * 0.5, this.world.height - 10);
      this.input.onDown.addOnce(() => {
          this.lifeLostText.visible = false;
          this.ball.body.velocity.set(150, -150);
      }, this);
    } else {
      alert('You lost, game over!');
      location.reload();
    }
  }

  startGame() {
    this.startButton.destroy();
    this.ball.body.velocity.set(150, -150);
    this.playing = true;
  }
}

const game = new Game('100', '100', Phaser.AUTO);