old_contents: import React, { Component } from 'react'
  
  import * as firebase from 'firebase'
  import config from '../../firebaseConfig'
  
  import Navbar from './Navbar'
  
  import { auth } from 'APP/db/firebase'
  
  //AppInstance.unsubscribe
  
  export default class App extends Component {
    constructor(props) {
      super(props)
  
    }
  
    componentDidMount () {
      this.unsubscribe = auth.onAuthStateChanged(function(user) {
        if (!user) auth.signInAnonymously()
        // .then( user => this.setState({user}))
        .catch(error => {
          console.log('ERROR', error.code, error.message)
        })
      })
    }
  
    componentWillUnmount () {
      this.unsubscribe()
    }
  
    render() {
      return (
        <div>
          <Navbar />
          <div>{ this.props.children }</div>
        </div>
      )
    }
  }
  
new_contents: import React, { Component } from 'react'
  
  import * as firebase from 'firebase'
  import config from '../../firebaseConfig'
  
  import Navbar from './Navbar'
  
  import { auth } from 'APP/db/firebase'
  
  //AppInstance.unsubscribe
  
  export default class App extends Component {
    constructor(props) {
      super(props)
  
    }
  
    componentDidMount () {
      this.unsubscribe = auth.onAuthStateChanged(function(user) {
        if (!user) auth.signInAnonymously()
        .catch(error => {
          console.log('ERROR', error.code, error.message)
        })
      })
    }
  
    componentWillUnmount () {
      this.unsubscribe()
    }
  
    render() {
      return (
        <div>
          <Navbar />
          <div>{ this.props.children }</div>
        </div>
      )
    }
  }
  
subject: Update App.js