mobx-websocket-store

A simple class to create a mobx store that uses atoms to open and close websocket connections based on the observed state of the store.

A note on Mobx 4.x

mobx-websocket-store 0.2.0 and above is compatible with MobX 4.x, however I strongly advise using Mobx 4's onBecomeObserved / onBecomeUnobserved hooks instead. See here for more info.

If you are using Mobx 3.x, you can use mobx-websocket-store 0.1.2 and below to achieve similar functionality.

Installation

Install with your package manager of choice

yarn add mobx-websocket-store
// or
npm install mobx-websocket-store

Motivation

The concept of this was driven by using the firebase realtime database in a frontend react project. A firebase database reference is analogous to having a 'socket', and attaching or detaching value listeners to that reference is analagous to opening and closing the socket connection.

A data store should therefore start listening to a reference only when one or more views were subscribed to that store. When all views are later removed, the store should stop listening for changes at that reference.

Usage

Constructor

constructor(
  openWebsocket: (store: MobxWebsocketStore<T>) => void, 
  closeWebsocket: (store: MobxWebsocketStore<T>) => void, 
  opts?: StoreOpts
);

Options

{
    id?: string; // An identifier that can be accessed by 'instance.id'
    resetDataOnOpen?: boolean; // Whether the store's cached data is reset when the socket is closed and reopened 
}

Instance Properties

const store = new MobxWebsocketStore( ... )

store.id // Gets the id passed in via opts
const data = store.data // Gets the store data and notifies the store it is being observed
store.data = ... // Sets the store data and notifies observers of update

Example

Create a store instance for your websocket using the constructor, and passing in an onOpenWebsocket and onCloseWebsocket callback and options:

import  MobxWebsocketStore from 'mobx-websocket-store';
import { autorun } from 'mobx';

const socket = ...
const store = new MobxWebsocketStore(
  (store) => {
    console.log("Opening websocket");
    socket = openSocket();
  },
  (store) => {
    console.log("Closing websocket");
    socket.close();
  },
  {
    id: 'MyStore',
    resetDataOnOpen: false
  }
);

autorun(() => {
  console.log(store.data);
});

Example With React and Firebase

Here's how you could set up a simple chat room in about 5 minutes, using the very excellent mobx-react bindings and the firebase package.

First, we'll set up a store that will fetch messages in the chat room when it is observed:

import MobxWebsocketStore from 'mobx-websocket-store';
import firebase from "firebase";

firebase.initializeApp( ... );

const ref = firebase.database().ref("/messages");
const refListener = (snapshot: firebase.database.DataSnapshot) => {
  this.data = snapshot.val(); // 'this' will be bound later to the MobxWebsocketStore context
  this.atom.reportChanged();
};

const store = new MobxWebsocketStore(
  (store) => {
    console.log("Opening websocket");
    ref.on("value", refListener.bind(store));
  },
  (store) => {
    console.log("Closing websocket");
    ref.off("value", refListener.bind(store));
  }
);

Then, by passing that store to a component as a prop, a react component can subscribe to that store like below:

@observer
class ChatRoom extends Component {
  render() {
    const messages = this.props.store.data;
    return (
      /* Render each message into a component */
    );
  }
}

And voila! Thanks to MobX atoms and a little MobX secret sauce, when a ChatRoom component is rendered, it will subscribe to the messages store, which will cause that store to start listening to that database reference. When the ChatRoom component stops being rendered, due to the user navigating elsewhere, the database reference will stop listening for changes.