问错误:无法设置标头发送后，SSR反应+节点

EN

Error: Can't set headers after they are sent

getActionButtons = () => {
    if(this.state.stepIndex > 2){
      return (<ActionButtons>
        <ActionButton label={this.state.userType === 'Rider' ? this.state.available ? 'Found a carpool?' : 'look for carpool' : this.state.available ? 'Car is Full?' : 'Available for carpool'} primary={!this.state.available} secondary={this.state.available} onClick={() => {
         console.log("eventId: ", this.props.eventId.event)
          console.log("userId: ", firebase.auth().currentUser.uid)
          // firebase.database().ref('/' + this.props.eventId.event + '/posts/' + firebase.auth().currentUser.uid).transaction((post => {
          //   if (post) {
          //     if (post.available) {
          //       post.available = !post.available
          //     } else {
          //       post.available = this.state.available
          //     }
          //   }
          //   return post;
          // }))
          firebase.database().ref('/' + this.props.eventId.event + '/posts/' + firebase.auth().currentUser.uid + '/available').set(!this.state.available)
          this.setState({
            available: !this.state.available
          });
          this.props.update();
        }}/>
      </ActionButtons>)
    }
  }

const activeRoute = routes.find(route => matchPath(req.url, route)) || {}
const isEventPage = activeRoute.name === "carpoolingPage"


app.get("*", (req, res, next) => {
if(isEventPage) {
    if (req.params[0]) {
      let eventRef = firebase.database().ref(req.params[0])
      eventRef.on("value", (snapshot) => {
        const event = snapshot.val()
        // console.log("event: ", event)
        if(!event)
          res.redirect("/eventnotfound")
        else {
          const { title, location, description } = event
          const preloadedState = { currentEvent: event }
          const store = configureStore(preloadedState)
          const markup = generateMarkup(store)
          res.send(HTML({
            title: `Carpooling to ${ title }`,
            markup, styleTags,
            preloadedState,
            ogTitle: `Carpooling to ${ title }`,
            ogDescription: `Find people to carpool with to ${ title }. Choose to ride or drive to ${ location } ${ description === null ? '' : `Event Description: ${ description }`}`
          }))
        }
      })
    }
  }
  else {
    const store = configureStore()
    const markup = generateMarkup(store)
    res.send(HTML({ markup, styleTags }))
  }
})