Redux Thunk Subscribe

Similar to Redux Thunk, but with subscribe available to thunks (in addition to dispatch and getState) so they can add listeners to the store on-the-fly.

Important note: if you just need asynchonous actions, you probably should be using Redux Thunk instead!

Usage

npm install --save redux-thunk-subscribe

var createStore = require("redux").createStore;
var thunkSubscribeEnhancer = require("redux-thunk-subscribe");

var store = createStore(reducer, thunkSubscribeEnhancer);

var thunkExclamationPoint = function () {
  return function (dispatch, getState, subscribe) {
    console.log("thunk!");
  };
};

store.dispatch(thunkExclamationPoint());

Motivation

Why make store.subscribe available to action creators (thunks)?

Redux is normally used to build UIs, which are "complete" applications in the sense that no code is expected to be supplied by the application's users. In a UI, the consumer of store.subscribe can simply be hard-coded (usually to React). Library code is different. Often, libraries expect users to supply certain pieces of code; a common example is an event handler where the user specifies a callback function. I like the Redux philosophy a lot, and in my opinion it is a good fit for library code. However, in library code, consumers of store.subscribe are not always known in advance, and, in some cases, they are intended to be defined by the library's users. This creates a problem: where does the library save the callbacks?

One option is to put the user-created callbacks in the Redux store, along with the other data. However, since the callbacks are not serializable, this breaks some nice features of Redux. Putting callbacks in the store also just feels wrong: the callbacks themselves are not really state per se, but rather observers of the state.

I think a better solution is to make store.subscribe available to action creators, so that they can set up store listeners (i.e., user-supplied callbacks) on-the-fly. That's what this library does. Since subscribe is not included in Redux's middleware API, this library is a store enhancer that changes the thunk signature from (dispatch, getState) to (dispatch, getState, subscribe).

Tests

npm test