Universal redux-saga server-side render

redux-saga-server-side-render.js

import R from 'ramda';
import ReactDOMServer from 'react-dom/server';
import { put, call } from 'redux-saga/effects';

const LOADING = 'LOADING';
const MAX_RENDERS = 10;

export function renderUntilDone(store, app) {
  return new Promise((resolve, reject) => {
    let again = true;
    let renderCount = 0;
    let html;

    const unsub = store.subscribe(onChange);
    onChange(true);

    function onChange(first = false) {
      const loading = store.getState().loading;
      if (!first && loading && loading.length) {
        again = true;
        return;
      }

      if (again) {
        again = false;
        render();
      } 

      // This may not work if onChange isn't called sync during render
      if (!again) {
        unsub();
        resolve(html);
      }
    }

    function render() {
      renderCount++;
      if (renderCount > MAX_RENDERS) {
        unsub();
        return reject(new Error(`Tried to render more than ${MAX_RENDERS} times.`));
      }

      const state = store.getState();
      html = ReactDOMServer.renderToString(app(state));
    }
  });
}

export function reducer(state = [], action) {
  if (action.type !== LOADING) return state;
  // no-dupes version
  // const mod = action.finished ? R.without([action.data]) : R.compose(R.uniq, R.append(action.data));
  const without = R.without([action.data]);
  const oneLess = R.compose(R.tail, R.filter(R.equals(action.data)));
  const removeOne = R.converge(R.concat, [without, oneLess]);
  const mod = action.finished ? removeOne : R.append(action.data);
  return mod(loading);
}

// Wrap your loading sagas with this function
export function *addLoading(type, func, ...args) {
  const data = [type, func, ...args];
  yield put({ type: LOADING, data });
  try {
    yield call(func, ...args);
  } finally {
    yield put({ type: LOADING, data, finished: true });
  }
}