redux-external-dispatchers

A Redux store enhancer to let non-Redux pieces of your application dispatch actions into Redux without also having access to Redux state.

Why should I use this?

On NPR.org, we embedded a Redux app into our broader non-Redux web site experience.

We found that middleware is an OK integration point between the Redux app and non-Redux concerns. However, middleware is a very powerful tool: it provides dispatch capabilities AND a window into Redux state.

When you just need to tell the Redux part of your app what the non-Redux part is doing, all you really need is dispatch. If you only need to dispatch, then you also don't need the overhead of executing middleware code on every action.

This can also help you keep a bright line between effectful code and pure code.

Examples

Browser document visibility

Bind a handler to the document's visibilitychange event that tells your Redux app whether it is visible to the user.

import BrowserActions from '../lib/Browser/actions';

let visibility = document.visibilityState;

export default function visibilityDispatcher({ dispatch }) {
  document.addEventListener('visibilitychange', function onResize() {
    const currentVisibility = document.visibilityState;
    if (currentVisibility !== visibility) {
      dispatch(BrowserActions.onVisibilityChanged(currentVisibility));
      visibility = currentVisibility;
    }
  });
};

Browser viewport breakpoint

Bind a handler to the window resize event that tells your Redux app what the current breakpoint is (mobile, tablet, desktop, etc.).

import BrowserActions from '../lib/Browser/actions';
import Breakpoints from '../lib/constants/Breakpoints';

function getBreakpointFromWidth(width) {
  if (width < 768) {
    return Breakpoints.SMALL;
  } else if (width < 1024) {
    return Breakpoints.MEDIUM;
  } else {
    return Breakpoints.LARGE;
  }
}

let breakpoint = getBreakpointFromWidth(window.innerWidth);

export default function viewportDispatcher({ dispatch }) {
  window.addEventListener('onresize', function onResize() {
    const currentBreakpoint = getBreakpointFromWidth(window.innerWidth);
    if (currentBreakpoint !== breakpoint) {
      dispatch(BrowserActions.onBreakpointChanged(currentBreakpoint));
      breakpoint = currentBreakpoint;
    }
  });
};

Content environment

Since we embedded a Redux app into an existing web site, we already had a tested non-Redux system for page navigation. To tell our app whether we were on a news page, music page, etc., we bound a handler to our page navigation event and dispatched an action notifying Redux about the content environment.

import $ from 'jquery';
import NavigationActions from '../lib/Navigation/actions';

export default function contentEnvDispatcher({ dispatch }) {
  window.addEventListener('hashchange', function onHashChange() {
    const environment = $('section.main-section').attr('id');
    dispatch(NavigationActions.onContentEnvironmentChanged(environment));
  });
};

Advertising integration

If you control the markup for advertising, you can bind an event handler to interactions on a non-Redux advertisement and notify the Redux app about them. This was one of the ways we supported playing sponsored content in our audio player app on the web site.

import AudioActions from '../lib/Audio/actions';

export default function adAudioDispatcher({ dispatch }) {
  document.addEventListener('app:ads:loaded', function () {
    const adIframe = document.querySelector('#ad iframe');
    if (adIframe && adIframe.contentDocument) {
      const audioElement = adIframe.contentDocument.querySelector('[data-ad-audio]');
      if (audioElement && audioElement.getAttribute('data-ad-audio')) {
        AudioActions.play(audioElement.getAttribute('data-ad-audio'));
      } 
    }
  });
};

Wiring to your Redux store

You hook this library into your app like any other store enhancer: as the third argument to Redux's createStore.

import { createStore } from 'redux';
import { applyExternalDispatchers } from 'redux-external-dispatchers';

import rootReducer from './reducer';
import { timer, message } from './external-dispatchers';

export default function configureStore(initialState) {
  return createStore(
    rootReducer,
    initialState,
    applyExternalDispatchers(timer, message),
  );
};

If you are already using one store enhancer, you will need to use Redux's compose to compose all of your store enhancers together.

Note: The order of applying store enhancers matters a lot!

Simple instructions

Make sure that your applyExternalDispatchers call is the first argument to compose.

import { createStore, applyMiddleware, compose } from 'redux';
import { applyExternalDispatchers } from 'redux-external-dispatchers';
import thunk from 'redux-thunk';
import createLogger from 'redux-logger';

import rootReducer from './reducer';
import { timer, message } from './external-dispatchers';

export default function configureStore(initialState) {
  return createStore(
    rootReducer,
    initialState,
    compose(
      applyExternalDispatchers(timer, message),
      applyMiddleware(thunk, createLogger())
    )
  );
};

Advanced instructions

The Redux store enhancer API requires that each store enhancer return a patched version of the store. The last argument of compose will modify the original Redux store. The second to last argument will patch the modified store, and so on.

One of the important consequences of this is that any Redux store API functions (dispatch, getState, subscribe, and replaceReducer) used within any given store enhancer will only have the features of previously applied store enhancers.

You most likely want your external dispatchers to have access to all of the enhancements provided by all of your other store enhancers.

Take the example of applyMiddleware in the code above. It will receive the original Redux dispatch and return a store whose dispatched actions will run through each middleware. As a result, applyExternalDispatchers will receive a dispatch function that passes through middlewares. Since applyExternalDispatchers injects the version of dispatch it receives during store creation, actions dispatched from external dispatchers will run through all middlewares.

Consider what would happen if we reversed the order of the compose arguments. applyExternalDispatchers would receive the original Redux dispatch and return a store with an unmodified dispatch. applyMiddleware would receive the unmodified dispatch and return a store whose dispatch function runs through all middlewares. The external dispatchers will only have a handle on the unmodified Redux dispatch.

Store enhancer resources

Dependencies

There is only a peer dependency on Redux 3.1.0 or later. Redux 3.1.0 introduced a nicer store enhancer API that made this project easier to integrate into existing Redux apps.

Acknowledgements

@justinbach: genesis of the external dispatcher concept and leadership for its implementation on NPR.org.

License

MIT

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