text: let instance
  
  /**
   * 统一的音效管理器
   */
  export default class Music {
    constructor() {
      if ( instance )
        return instance
  
      instance = this
  
      this.bgmAudio = new Audio()
      this.bgmAudio.loop = false
      this.bgmAudio.src = 'audio/boom.mp3'
  
      this.shootAudio     = new Audio()
      this.shootAudio.src = 'audio/bullet.mp3'
  
      this.boomAudio     = new Audio()
      this.boomAudio.src = 'audio/boom.mp3'
  
      this.playBgm()
    }
  
    playBgm() {
      this.bgmAudio.play()
    }
  
    playShoot() {
      this.shootAudio.currentTime = 0
      this.shootAudio.play()
    }
  
    playExplosion() {
      this.boomAudio.currentTime = 0
      this.boomAudio.play()
    }
  }
  