小程序app.onLaunch中获取用户信息，index.onLoad初次载入时取不到值的问题

//app.js
App({
  globalData:{
    nickname:''
  },
  onLaunch: function () {
    let that=this;
    //假设已经授权成功
    wx.getUserInfo({
        success(res){
            //获取用户信息并赋值给globalData
            that.globalData.nickname=res.userInfo.nickName;
        }
    })


  }
})

//index.js
const app = getApp()
Page({
  data: {
    myNickName:''
  },
  onLoad: function (option) {
    console.log(app.globalData.nickname); //结果："" 
    this.setData({
        myNickName:app.globalData.nickname
    })
    //由于wx.getUserInfo()是异步请求，不知道什么时候成功返回数据，导致获取失败
  }
})

//app.js
App({
  globalData:{
    nickname:''
  },
  onLaunch: function () {
    let that=this;
    //假设已经授权成功
    wx.getUserInfo({
      success(res) {
        let tmp=res;
        
        setTimeout(()=>{//更清楚的模拟异步环境，设置5秒后执行代码
          //获取用户信息并赋值给globalData
          that.globalData.nickname = res.userInfo.nickName;
          if (that.userInfoReadyCallback) {
            console.log('call back')
            that.userInfoReadyCallback(res.userInfo.nickName)
          }
        },5000)

      }
    })

  }
})

//index.js
const app = getApp()
Page({
  data: {
    myNickName:''
  },
  onLoad: function (option) {
    let that = this;
    let mynickname = app.globalData.nickname;
    //如果app.onLaunch中的wx.getUserInfo()返回够快
    //在app.onLoad之前就已经初始化了app.globalData.nickname则直接更新本界面的this.data.nickname
    if(mynickname.length){
      this.setData({
        nickname:mynickname
      })
    //定义回调函数，一旦app.onLaunch的wx.getUserInfo获取到用户信息的时候，立即运行该回调函数
    }else{
      app.userInfoReadyCallback=res=>{
        this.setData({
          nickname:res
        })
      }
    }
  }
})