FSA-compliant promise middleware for Redux.

npm install --save redux-promise

import promiseMiddleware from 'redux-promise';

The default export is a middleware function. If it receives a promise, it will dispatch the resolved value of the promise. It will not dispatch anything if the promise rejects.

If it receives an Flux Standard Action whose payload is a promise, it will either

• dispatch a copy of the action with the resolved value of the promise, and set status to success.
• dispatch a copy of the action with the rejected value of the promise, and set status to error.

The middleware returns a promise to the caller so that it can wait for the operation to finish before continuing. This is especially useful for server-side rendering. If you find that a promise is not being returned, ensure that all middleware before it in the chain is also returning its next() call to the caller.

Because it supports FSA actions, you can use redux-promise in combination with redux-actions.

This works just like in Flummox:

createAction('FETCH_THING', async id => {
  const result = await somePromise;
  return result.someValue;
});

Unlike Flummox, it will not perform a dispatch at the beginning of the operation, only at the end. We're still looking into the best way to deal with optimistic updates. If you have a suggestion, let me know.

Say you have an API module that sends requests to a server. This is a common pattern in Flux apps. Assuming your module supports promises, it's really easy to create action creators that wrap around your API:

import { WebAPI } from '../utils/WebAPI';

export const getThing = createAction('GET_THING', WebAPI.getThing);
export const createThing = createAction('POST_THING', WebAPI.createThing);
export const updateThing = createAction('UPDATE_THING', WebAPI.updateThing);
export const deleteThing = createAction('DELETE_THING', WebAPI.deleteThing);

(You'll probably notice how this could be simplified this even further using something like lodash's mapValues().)