example

index.js

class App extends Component {
  constructor(){
    this.state = {loading: true}
  }
  componentWillMount(){
    FCMToken(token){
      this.setState({token: token, loading: false})
    }
  }
  render(){
    if(this.state.loading){
      return null
    }else{
      return <WebView url={{url:`http://example.com?token=${this.state.token}`}}>
    }  
  }
}