effects-middleware

simple redux middleware to let other middleware (plugins) dispatch actions with side-effects

The idea and code are originally from the Hyper JS terminal emulator by Zeit. This is just an effort to make it available as a standalone module. When creating a redux-based plugin system (as in Hyper), plugins can hook into events via a middleware export, which checks for certain action types and acts on them. In the words of the Hyper code comments: "It allows authors to interrupt, defer or add to existing side effects at will as the result of an action being triggered." And from the Hyper docs:

This means that you can override, compose or completely eliminate effects! In other words, this is how you can change the default functionality or behavior of the app.

How to Use

First install as normal

npm install --save effects-middleware

You'll want to make sure to load any plugin middleware before the effects middleware so that they can act on the actions first.

// ./store/index.js
import {createStore, applyMiddleware, compose} from 'redux';
import thunk from 'redux-thunk';
import effects from 'effects-middleware';

import { myMiddleware } from '../utils/middleware';
import rootReducer from './reducers'

const enhancer = compose(applyMiddleware(thunk, myMiddleware, effects));

export default createStore(rootReducer, enhancer);

Next let's create an action creator that when dispatched should have a side effect.

export function activateSideEffect() {
  return ({ dispatch, getState }) => {
    dispatch({
      type: 'ACTIVATE_SIDE_EFFECT',
      effect() {
        const { foo } = getState();
        console.log('Side effect was executed. Here is the foo state: ', foo);
        dispatch({
          type: 'SOME_OTHER_ACTION',
          payload: '42'
        })
      }
    });
  }
}

Now if you dispatch the action activateSideEffect...

dispatch(activateSideEffect())
// Side effect was executed. Here is the foo state: ...

... you should see the results of your side effect.