Redux-elm-middleware NPM

redux-elm-middleware

Elm middleware for redux :sparkles:

Installation

You need to install redux-elm-middleware for js and elm.

$ npm i redux-elm-middleware -S

Redux-elm-middleware is currently only published to npm. You will need to add the following to you elm-package.json

  "source-directories": ["node_modules/redux-elm-middleware/src", ...]

Usage

Setup Redux Middleware

import createElmMiddleware from 'redux-elm-middleware'
import { reducer as elmReducer } from 'redux-elm-middleware'

// Import your Elm Reducer
import Elm from '../build/elm'

const reducer = combineReducers({
  elm: elmReducer
  // ...middlewares
})


// create a worker of your elm reducer
const elmStore = Elm.Reducer.worker();

// create the middleware
const { run, elmMiddleware } = createElmMiddleware(elmStore)

// create the redux store and pass the elmMiddleware
const store = createStore(reducer, {}, compose(
  applyMiddleware(elmMiddleware),
  window.devToolsExtension ? window.devToolsExtension() : f => f
));

// you need to run the elm middleware and pass the redux store
run(store)

Elm root reducer

The root reducer from redux-elm-middleware simply takes all actions from your elm reducers and returns the payload as the next state.

The new model returned in your elm reducers update function is dispatched as a new action to the redux store.

f.e.

{
  type: '@@elm/Increment',
  payload: {
    counter: 3
  }
}

Creating a Reducer in Elm

A reducer in elm looks like a normal TEA module without the view.

port module Reducer exposing (Model, Msg, init, update, subscriptions) -- Name of the module must match the worker


import Redux

-- define ports for all actions which should be handled by the elm reducer
port increment : ({} -> msg) -> Sub msg

-- define all subscriptions of your reducer
subscriptions : Model -> Sub Msg
subscriptions _ =
    Sub.batch
        [ increment <| always Increment
        -- ...
        ]

-- In order for the Elm model to cross the border safely it must be encoded as a JSON value.
encode : Model -> Json.Encode.Value
encode model =
    ...

-- MODEL
-- UPDATE

-- START THE REDUCER
main =
    Redux.program
        { init = init
        , update = update
        , encode = encode
        , subscriptions = subscriptions
        }

Motivation

write bulletproof businesslogic
handle state and effects
- pure
- in one place
- with a safetynet
still have the rich react/redux ecosystem at your paws
- components
- middlewares
  - routing
  - persistent state (localstorage)
  - offline support
  - ui state ( redux-ui )
sneak a nice functional language into your projects
don't have to commit 100% to it
slowly convert a redux/react app into elm