微信小程序Cannot read property 'play' of undefined

微信小程序

为什么会报错呢？

Page（{
initialAudio:function(){
     let bgAudioManager=this.bgAudioManager
     bgAudioManager.title='停顿'
     bgAudioManager.epname='停顿'
     bgAudioManager.singer='赵乃吉'
     bgAudioManager.coverImgUrl='https://y.qq.com/mediastyle/yqq/img/player_logo.png?max_age=2592000'
     bgAudioManager.src='http://dl.stream.qqmusic.qq.com/C400002PhC6r2R8yda.m4a?guid=5435628059&vkey=256CA3C8F5BC221E409E3C612A666EE68000BEDD31A83897A1299B8FC07A159C1883F518A34D21F73F161F75CBA37F2A0A4406619F16BB8C&uin=1152921504992073674&fromtag=66'
   },
   play:function(){
     var that=this
     this.bgAudioManager.play()
   },
   pause:function(){
     var that=this
      this.bgAudioManager.pause()
   },
   onLoad:function(options){
     this.bgAudioManager=wx.getBackgroundAudioManager()
     this.initialAudio()
   },
}）