redux-echos

A lightweight redux middleware to decouple and serialise state dependencies.

This sounds awful. Or a better version:

It helps to deal with the to-be-laterly-dispatched actions.

Scenarios

• state dependency
• action workflow

Examples

First of First, but not actually

Apply echos as a middleware to the redux store.

import echos from 'redux-echos'
import { createStore, applyMiddleware } from 'redux'
 
const store = createStore(reducer, applyMiddleware(echos))

note-1: this step may be safely skipped sometimes when redux-thunk is here and you would dispatch all echo actions manually.

note-2: If note-1 does not make clear sense for you, applying the middleware is a safer option.

Action Forking

An action, in its reducer, may spawn other action(s) now.

import { echo } from 'redux-echos'
 
const reducer = (state, action) => {
  if (action.type === 'The/Source/ACTION') {
    echo({
      type: 'An/Echo/ACTION',
      some: state.an.important.value
    }, action)
    return {...state, key: 'new-value'}
  }
  return state
}

And of course, the function echo() can also be called out of a reducer to queue an action.

Action Chain

Instead of emitting one or several independent actions, you can make a series of actions, which can have thunks, to be dispatched sequentially.

import { chain } from 'redux-echos'
 
const reducer = (state, action) => {
  if (action.type === 'User/Is/AUTHENTICATED') {
    chain(
      NetworkActions.loadUserProfile(), action
    )(
      NetworkActions.loadFriendProfiles()
    )
    return {...state, key: 'new-value'}
  }
  return state
}

And if all actions in a chain are common object actions, like:

chain(A1)(A2)(A3)...

works exactly like:

echo(A1); echo(A2, A1); echo(A3, A2); ...

But if there is a thunk, e.g: A1, then A2 will only be dispatched after A1's resolved action has been dispatched.

If the resolved action is still a thunk, A2 will continue to wait recursively until a final action is dispatched.

note-1: currently, redux-echos only supports redux-thunk.

note-2: if the source action is not empty, for example:

chain(A1, A0)(A2)(A3)...

can be coded as:

import { follow } from 'redux-echos'
follow(A0)(A1)(A2)(A3) ...

since the A0 is taken as the source action, follow(...) will not try to dispatch it.

note-3: if you need more complex workflow like feature of forking & merging, please refer to redux-action-flow

Action Translating

A state may associate itself with another one which it depends on.

import { listen } from 'redux-echos'
 
const translator = (action, state) => ({
  type: 'An/Echo/ACTION',
  some: state.an.important.value
})
 
listen('The/Source/ACTION', translator)

or apply a selector to help the translator

const translator = (action, value) => ({
  type: 'An/Echo/ACTION',
  some: value
})
 
const selector = state => state.an.important.value
 
listen('The/Source/ACTION', translator, selector)

Coding Practice

• w/ or w/o redux-thunk
• reducer-centred code organising.
• analyse action flow.

API Reference

Basics

They should be enough for common scenarios.

default exports: middleware(store) => (next) => (action)

the middleware

echo(action, source)

generate an echo action for an target action.

chain(action[, source])

create an action chain from an action with an optional source action.

follow(source)

create an action chain from an source action.

listen(actionType, translator[, selector])

listen to a type of action to apply a translator to generate none, one or more forked actions.

Advanced

They should be used with a little bit carefulness.

thunk(action[, source]) => (dispatch)

explicitly create a thunk as the echo action for an optional source action.

squeak(action[, source])

explicitly create an common object echo action for an optional source action.

create(action[, source])

automatically create a thunk or an object by the existence of redux-thunk.

echos()

peek all current queued echo actions.

thunkEnabled()

query if the thunk mode is enabled.

enableThunk()

explicitly to enable thunk mode.

disableThunk()

explicitly to disable thunk mode.

translators([actionType])

peek all listening translators (as an object of action-type -> array-of-translator map) or an array of translators for the actionType.

unlisten(translator[, actionType])

remove a translator from all actions or a particular action.

Tour of Implementation

• Why not Observable?
• Design Principles
• Performance Concerns

The Last Of Last, actually

In this document, the word state is actually used with the meaning of sub-state since it is not referring the root state of the redux store.