微信小程序 使用回调函数解决index的onLoad先于onLaunch返回数据的问题

app.js

// app.js
App({
  sessionCallBack:null,
  onLaunch() {
    // 展示本地存储能力
    const logs = wx.getStorageSync('logs') || []
    logs.unshift(Date.now())
    wx.setStorageSync('logs', logs)
    // 登录
    wx.login({
      success: res => {
        var code = res.code
        wx.getUserInfo({
          success: res=>{
            console.log("用户信息：",res)
            getApp().globalData.userInfo = res.userInfo
            console.log(getApp().globalData.userInfo)
            wx.request({
              url: getApp().globalData.url + 'english/login',
              method: 'POST',
              header: {
                'content-type': 'application/x-www-form-urlencoded'
              },
              data:{
                code: code,
                encryptedData: res.encryptedData,
                iv: res.iv,
              },
              success:(res)=>{
                console.log(res)
                wx.setStorageSync('session', res.data.rd_session)
                wx.setStorageSync('type', res.data.type)
                if(this.sessionCallBack){   // 此回调函数将在index.js中被定义
                  this.sessionCallBack(res.data.rd_session)
                }
              },
            })
          }
        })
      }
    })
  },
  globalData: {
    userInfo: null,
    url : "http://127.0.0.1:8000/"
  }
})

index.js

onLoad() {
    var session = wx.getStorageSync('session')
    if (!session){
      getApp().sessionCallBack=(session)=>{
        if(session){
          this.nav()
        }
      }
    }
    else{
      this.nav()
    }
  },