Hi, I'm Simon.

Simon Fletcher is a 24 year old British software engineer currently working with JavaScript at Minbox in San Francisco, CA.

Previously, he was a founder at Y Combinator funded Interstate (acquired by Stripe).

Rendering asynchronous React components with redux-interceptor
May 3rd 2016

Rendering a React component on the server often requires asynchronously fetching any data which the component or any of its children require. If you're using Redux to store and fetch your data, you can easily solve this problem through a small piece of middleware. The trade-off with using this method is that you will suffer the slight performance penalty of rendering your React application twice but this shouldn't be a problem for most applications.

The middleware we'll use to solve this problem, redux-interceptor, intercepts and records any store actions that are dispatched so that they can be executed in a single batch at a later time. We can take advantage of the middleware by placing all essential data fetching in the componentWillMount lifecycle method. This method is called during both client and server renders which means on the server, you're able to capture all the necessary actions your component tree requires, wait until they resolve and then re-render your application with a hydrated store.

I've published the middleware on GitHub: http://github.com/simonify/redux-interceptor and you can install it via npm install react-interceptor --save.

Here's an example of how to use it:

import React, { Component, PropTypes } from 'react';
import { renderToString } from 'react-dom/server';
import { applyMiddleware, createStore } from 'redux';
import { Provider, connect } from 'react-redux';
import thunk from 'redux-thunk';
import createInterceptor from 'redux-interceptor';

const FETCH_RANDOM = 'example/FETCH_RANDOM';
const SET_RANDOM = 'example/SET_RANDOM';

const fetchRandom = () => dispatch => {
  dispatch({ type: FETCH_RANDOM });

  return new Promise((resolve) => setTimeout(() => resolve(dispatch({
    type: SET_RANDOM,
    payload: Math.random()
  })), 2500));

function reducer(state = { fetching: false, random: null }, action) {
  switch (action.type) {
    case FETCH_RANDOM:
      return { ...state, fetching: true, random: null };
    case SET_RANDOM:
      return { ...state, fetching: false, random: action.payload };
      return state;

class App extends Component {
  static propTypes = {
    fetchRandom: PropTypes.func.isRequired,
    random: PropTypes.number

  componentWillMount() {
    if (typeof this.props.random !== 'number') {

  render() {
    return (
        {typeof this.props.random === 'number' ? this.props.random : 'Loading...'}

const interceptor = createInterceptor();
const store = createStore(reducer, applyMiddleware(interceptor, thunk));
const ConnectedApp = connect(({ random }) => ({ random }), { fetchRandom })(App);
const render = () => renderToString((
  <Provider store={store}>
    <ConnectedApp />

// <div data-reactroot="" data-reactid="1" data-react-checksum="622727842">Loading...</div>

// <div data-reactroot="" data-reactid="1" data-react-checksum="-1584000246">0.9193182914256697</div>