class Example extends Phaser.Scene {
  preload() {}

  create() {
    const circle = this.add.circle(100, config.height / 2, 10, 0xffffff);
    this.tweens.add({
      targets: circle,
      x: 600,
      duration: 3000,
      repeat: -1
    });
  }
}

const config = {
  type: Phaser.AUTO,
  transparent: true,
  width: 800,
  height: 400,
  scene: Example
};

const game = new Phaser.Game(config);