hzzzzl

this.eventSource = new EventSource("http://localhost:5000/api/......")

  componentDidMount() {
    ......
    this.subscribeToServerEvent()
  }

  subscribeToServerEvent = () => {
    this.eventSource.onmessage = e => {
      try {
        ......
        this.setState({ ..... })
      } catch (e) {
        console.log('error parsing server response', e)
      }
    }
  }

this.timeout = setInterval(() => {
      this.setState({ value: this.state.value + this.props.speed });
      this.nanobar.go(this.state.value);
    }, 1000);

<Route 
  path='/publishedArticlePage' 
  render={ (props) => <PublishedArticlePage {...props} article={article} } 
/>

state = { loaded: false, data: null }

const getData = () => new Promise(resolve => {
  setTimeout(() => resolve( {data: 177} ), 2000)
})

...

getData().then(d => {
  // что то делаем с данными, например
  this.setState( { loaded: true, data: d } )
})

render() {
  if (!this.state.loaded) return <Loading />
  return <MyBeautifulDataComponent />
}