redux-loop.js

const createInstance = () => {
  const queue = [];

  return {
    schedule: effect => queue.push(effect),
    getQueue: () => queue
  };
};

const NoOp = {
  schedule: () => {},
  getQueue: () => []
};

let instance = NoOp;

const loop = (state, effect) => {
  instance.schedule(effect);
  return state;
};

const withEffects = cb => {
  const prevInstance = instance;
  instance = createInstance();
  cb();
  const queue = instance.getQueue();
  instance = prevInstance;
  return queue;
};

const nextTick = fn => Promise.resolve().then(fn);

const isPromise = value => value instanceof Promise;

const loopMiddleware = store => next => action => {
  const onError = store.onError || (() => {});

  const effects = withEffects(() => next(action));
  if (effects.length > 0) {
    nextTick(() => {
      effects.forEach(effect => {
        try {
          const result = effect(store);
          if (result && isPromise(result)) {
            result.catch(e => onError(e));
          }
        } catch (e) {
          onError(e);
        }
      });
    });
  }
};