Redux-observable?

Any thought on adding redux-observable support?

Could look something like:

@kea({
    key: (props) => props.id,

    path: (key) => ['scenes', 'homepage', 'slider', key],

    actions: () => ({
        updateSlide: index => ({ index })
    }),

    reducers: ({ actions, key, props }) => ({
        currentSlide: [props.initialSlide || 0, PropTypes.number, {
            [actions.updateSlide]: (state, payload) => payload.key === key ? payload.index % images.length : state
        }]
    }),

    selectors: ({ selectors }) => ({
        currentImage: [
            () => [selectors.currentSlide],
            (currentSlide) => images[currentSlide],
            PropTypes.object
        ]
    }),

    epic: (action$, store, selectors) => action$
        .ofType(SOMETHING_INIT)
        .map(() =>
            selectors.getSlideImages(store.getState()) 
        )
        .map(images => ({
            ...images,
            ...getSlideMetaData(store.getState(), images.cardSelection)
        }))
        //..etc...
})

[mariusandra]

Hey, starting with v0.25, kea-saga is now a separate package and all redux-saga code has been ripped out of the main package.

I also added a kea-thunk package.

Next step: create a kea-observable package and add support for epics!

[mariusandra]

So I read through the docs of RxJS and redux-observable.

I can definitely see how it’s an attractive alternative to redux-saga. Of course implementing it has some issues. The biggest ones:

1. Bundle size and redux-saga.

I’m quite sure that making rxjs a required dependency is a no-go. At the same time, if you use redux-observable, you might want to omit redux-saga from your bundle.

While we’re at it, could we make Kea flexible enough to add new side-effect libraries in the future? I’m sure that with redux-observable we haven’t seen the end of it.

Thus I’m favouring some sort of plugin system. But then, how to implement it? How to opt in to the features you want? How to know what you even want? 😃.

I need to revisit the current code and think of ways to achieve this. It is in dire need of some refactoring anyway. In fact, I already started with refactoring the low hanging fruits.

I believe in the end it should be as simple as

// in your root index.js
import 'kea-saga'
import 'kea-epic' // or kea-observable?

// elsewhere in the code
import { kea } from 'kea' // and use normally

2. When and how to start and stop epics?

Assuming epics are injected into Kea properly, we get into the nitty gritty of how to use them. Here’s where I’ll need help the most.

The main issue is related to starting and stopping epics as components are mounted/unmounted. I think I have an idea how to do it

Starting is probably easy. Here’s how it’s done for the Sagas - I create a channel, onto which kea sends all sagas that need to be started. The sagas themselves pay attention to if they’re already running or not.

Then when the component unmounts, I send a cancel event on the same channel.

How to do it with observables? I guess something similar would work? How to assure that only one instance of a observable is running?

Are there any common ways to stop observables, other than .takeUntil(action$.ofType("@@kea/unmounted/scenes.homepage.index"))?

3. Syntactic sugar

With sagas, in Kea you can do yield this.get('nameOfSelector') and that’s syntactic sugar for yield select(this.selectors.nameOfSelector). Should we have anything similar for redux-observable?

As by your example, we’d be anyway passing both the store and selectors to the epic, we could as well combine them into a “select” function, e.g.:

    // select = (selectorName) => selectors[selectorName](store.getState())

    epic: (action$, store, select) => action$
        .ofType(SOMETHING_INIT)
        .map(() =>
            select('slideImages')
        )
        .map(images => ({
            ...images,
            ...select('slideMetadata')
        }))
        //..etc...

… and/or how to give to the epic the created actions? Perhaps something like:

    // select = (selectorName) => selectors[selectorName](store.getState())

    epic: ({ actions, select }) => (action$, store) => action$
        .ofType(actions.initAction)
        .map(() =>
            select('slideImages')
        )
        .map(images => ({
            ...images,
            ...select('slideMetadata')
        }))
        .delay(1000)
        .map(image => actions.doSomethingToImage(image))
        //..etc...

… or to simplify the first line like:

    epic: ({ actions, select, action$, store }) => action$

… ? 😃

As I haven’t used redux-observable, I don’t know what is the best way forward here. I need to play around with it. So all sort of feedback is welcome! 😃