server-router.jsx

// @flow
import React from 'react'

export default class Router extends React.PureComponent {

  constructor(props) {
    super(props)
    this.state = {}
  }

  componentDidMount() {
    this.fetch(this.props.location.pathname).then(data => this.setState({ data }))
  }
    
  componentWillReceiveProps(nextProps) {
    if (this.isLocationEqual(this.props.location, nextProps.location)) return
    console.log('Page: location changed to:', this.props, nextProps)
    this.setState({ data: null }) // loading
    this.fetch(nextProps.location.pathname).then(data => this.setState({ data }))
  }
    
  render() {
    if (!this.state.data) return this.renderLoadingComponent(this.props)
    return this.renderComponent({ ...this.props, ...this.state.data }) // this function also takes care of sending headers, HTTP code, etc.
  }
}