Redux Elm Subscriptions

Listen to global events Elm Style.

npm i -S redux-elm-subscriptions

Why?

When creating components you most likely wanna keep your components dumb and not use lifecycle hooks which couples rendering to functionality. This package revolves around the idea that some of the events you listen to are global and come from a world "outside" of your application like:

• global mouse events
• timers and animation frame callbacks
• window focus and blur etc.
• listening to websocket messages

So instead of this in a component file ...

componentDidMount() {
  document.addEventListener('keydown', handlekeyDown);
}


componentWillUnmount() {
  document.removeEventListener('keydown', handlekeyDown);
}

you can do this in a central place in your code ...

import { createSubsriptions, subNone } from 'redux-elm-subscriptions';

...

// will be called every time the state changes
const mapStateToSubs = (state, dispatch) => {

  // each subscription function needs to set up the subscription and return
  // a function to unsubscribe
  const arrowKeysSub = () => {
    const handler = e => {
      if (e.keyCode === 32) {
        dispatch({ action: 'SPACE_PRESS' });
      }
    };
    document.addEventListener('keydown', handler);
    return () => {
      document.removeEventListener('keydown', handler);
    };
  };

  const listenToClicks = () => {
    const handler = () => { dispatch({ type: 'DOCUMENT_CLICK' }); };
    document.addEventListener('click', handler);
    return () => { document.removeEventListener('click', handler); };
  };

  // return an object of subscriptions
  return {
    arrowKeys: arrowKeysSub,
    anotherSubscriptions: () => {
      // subscribe here
      return () => {
        // unsubscribe here
      };
    },
    // only listen to clicks when the modal is open
    documentClick: state.modalOpen ? listenToClicks : subNone,
  };
};

// add them to the store
store.subscribe(createSubscriptions(store)(mapStateToSubs));

Also check out the example.

Some Details

The API is designed so you can control listening behavior based on your state. Your subscription function receives the state and dispatch as parameters and should start listening to some event in the world. After that it needs to return a function to unsubscribe from the event you just started listening to. The function will be called every time the state changes. If a subscription is no longer present in the returned object, the unsubscribe function will be called automatically.

As long as yo make sure that your functions return functions to unsubscribe, everything should be handled automatically for you.

What not to use it for?

This lib was build to listen events which happen outside the scope of your app. Don't use it for one-time things are things that involve performing other work. Those will be better served by a library like redux-loop. Examples that are not subscriptions but effects include:

• making http requests
• reading from the localStorage

Also, of course the subscriptions are only for global events. DOM Events that happen within the virtual DOM that is managed by your app, should be handled directly in your components.

How does it work?

Check out the source. It's very simple, less than 30 LOC and needs no dependencies.