routeEvents.jsx

import React from 'react'

class App extends Component {
  state = {error: false}
  
  componentDidMount() {
    fetch(url)
    .then(() => {
      // do something
    })
    .catch(error => {
      this.setState({error: true), () => Router.push(url)}
    })
  }
  
  componentWillUnmount() {
    // Unsubscribe here
      if (this.state.error)
        this.props.showAlert("fetch failed")
  }
  
  render () {
    return (
      <div>My App</div>
    )
  }
}