xstream-connect

higher order component to plug xstream as a store with React components

Install

yarn add react react-dom prop-types xstream @seracio/xstream-connect

Disclaimer

This package feets well the way we work and the problems we face (small size stores but complex async workflow on derived data). It's mostly intended to our own developments and is not well tested, the paradigm it relies on is....

The purpose here is not to provide an async middleware to a redux store with Streams, as redux-cycle-middleware and redux-observable do but to replace redux and its different slices (async middlewares, reducers and derived data) with (Memory)Streams. As this, we can express each variable of the store as a function of other variables, in a clean and async way.

xstream's Streams are the perfect tool to achieve this goal, as they are hot and can easily be transformed into MemoryStreams (via the remember method). xstream is also light and fast, with a simple and comprehensive API compared to other FRP libs.

This library only exposes a component Provider and an higher order function connect to connect your store to the React layer in a react-redux fashion.

Basic example

import React from 'react';
import ReactDOM from 'react-dom';
import xs from 'xstream';
import {connect, Provider} from '@seracio/xstream-connect';

// A store is just a dictionary of exposed Streams
const store = {
  count$: xs.periodic(1000).startWith(0),
  hello$: xs.of('hello')
};

const App = ({count, hello}) => { 
  return <div>{this.props.count} --- {this.props.hello}</div>;
}

// the combinator defines which part of your store 
// will be exposed and realised the mapping from Streams to props
const combinator = state => {
  const {count$, hello$} = state;
  return xs.combine(count$, hello$).map([count, hello] => ({count, hello}));
}

// We use a Higher order function connect to wrap our component and plug its props to the store values
const Connected = connect(combinator)(App);

ReactDOM.render(
  <Provider store={store}>
    <Connected />
  </Provider>,
  document.querySelector('#root')
);

Principles

Store and the Provider component

With this architecture, all the logic resides in Streams, the store props of the Provide component is just a hash/dictionary of Streams (or static values) you want to expose to the React layer.

// main.js
import React from 'react';
import ReactDOM from 'react-dom';
import {Provider} from '@seracio/xstream-connect';
import * as store from './store'; // <---- your store is just a dictionnary of exposed Streams

ReactDOM.render(
  <Provider store={store}> {/* <-- plugged your store to the React layer */}
    <Connected />
  </Provider>,
  document.querySelector('#root')
);

The connect function

In the previous versions of this lib (<3.x.x), the connect function was less complicated but also far less powerful and more "magical" (in the wrong way of the term).

The connect function takes a single function as param. This function, called the combinator, expressed two things:

• what part of the store our component will subscribe to
• and when will it receive props updates

To put it another way, the combinator receives the Provider's store and will return a new Stream that combine the part of the store we want our component to be aware of.

For example:

state => {
  const {list$, selected$} = state;
  return xs
    .combine(list$, selected$)
    .map([list, selected] => ({list, selected}));
}

or if you only want props to update when selected$ changes, you can use a sampleCombine

state => {
  const {list$, selected$} = state;
  return selected$
    .compose(sampleCombine(list$))
    .map([selected, list] => ({selected, list}));
}

or if you only want props to update when selected$'s id changes

state => {
  const {list$, selected$} = state;
  return selected$
    .compose(dropRepeats(isIdEqual))
    .compose(sampleCombine(list$))
    .map([selected, list] => ({selected, list}));
}

What matters is to return a Stream that has a dictionary as value. This dictionary will be merged with the props of the enhanced component.

How to dispatch actions from the React layer to the store?

There is no canonical way to achieve this. For instance, you can do as this:

• in your store, expose a dispatcher$ Stream of Stream, as this the React layer will have a Stream to send actions through.
• in your store, create an actions$ Stream that flatten dispatcher$

// store index.js
import _ from 'lodash/fp';
import xs from 'xstream';

// Our dispatcher is exposed 
export const dispatcher$ = xs.of(xs.create());
// actions are not
const actions$ = dispatcher$.flatten();

// little helper
// to check if an action is of a certain type
const isType = type => _.flow(_.get('type'), _.isEqual(type));

// an exposed Stream that depends on an action
export const counter$ = actions$
  .filter(isType('increment'))
  .fold(acc => acc + 1, 0)
  .startWith(0);

• expose your store into the React layer context

// main.js
import {Provider} from '@seracio/xstream-connect';
import * as store from './store'; // dispatcher$ is exposed 

// ...

• via the connect method to actionsProvider$, retrieve a Stream into your component's props:

// components/MyComponent.js
import xs from 'xstream';
import sampleCombine from 'xstream/extra/sampleCombine';
import {connect} from '@seracio/xstream-connect';

const MyComponent = ({counter, dispatcher}) => {
  // here, the dispatcher's value is a Stream, so we can, shamefully, send actions through it
  const increment = () => dispatcher.shamefullySendNext({type: 'increment'}); 
  return (
    <div onClick={increment}>{counter}</div>;
  );
};

// create a combinator function
const combinator = (state) => state.counter$
  .compose(sampleCombine(state.dispatcher$))
  .map(([counter, dispatcher]) => ({counter, dispatcher}));

// plug the component with the store
export default connect(combinator)(MyComponent);

Caveats

• Be aware that the HOC will wait for the first value of the combinator's Stream before rendering its wrapped component. Its render method will return null before or a default component if defined (not yet documented).
• Because of this... specificity, you should not hesitate to use default values with your Streams (at least in the combinator).
• Remember the remember method, it will transform your Stream into a MemoryStream, an RxJS BehaviorSubject, kind of.

Why don't you use cycle.js?

cycle.js is neat, but we kinda like the React ecosystem... and are also tired of the growing complexity of the redux layer when you want to manage asynchronicity.

License

MIT License

Copyright (c) 2017 serac.io

Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.