`createReducer()`

Creates a reducer on steroids. Reducer is a function that takes the previous state and an event and returns a new state.

Definitions
Usage
- on()
- off()
- reset()
- has()
- createEvents()

Definitions

type EventHandler<State, Payload, Meta> = (state: State, payload: Payload, meta: Meta) => State

type createReducer = <S>(
  initialState: Partial<S>,
  handlers: { [K: string]: EventHandler }
) => Reducer

type AnyEvent = EventCreator | string | Array<EventCreator | string>

type Reducer<State> = {
  (state: State, event: Event): State
  on(event: AnyEvent, handler: EventHandler): Reducer<State>
  off(event: AnyEvent): Reducer<State>
  reset(event: AnyEvent): Reducer<State>
  has(event: EventCreator | string): boolean
  createEvents(model: { [K: string]: EventHandler }): { [K: string]: EventCreator }
}

Usage

import { createEvent, createReducer } from 'stapp'

const increment = createEvent()
const reducer = createReducer(0)
  .on(increment, state => state + 1)

const state = reducer() // 0
const nextState = reducer(state, increment) // 1

`on()`

Attaches an EventHandler to the reducer. Adding handlers of already existing event types will overwrite previous handlers. Returns reducer.

import { createEvent, createReducer } from 'stapp'

const double = createEvent('Double state')
const add = createEvent('Add value')
const anotherAdd = createEvent('Add string', (x) => +x)

const reducer = createReducer(0)
  .on(double, (state) => state * 2) // Single event creator
  .on([add, anotherAdd], (state, payload) => state + payload) // An array of event creators
  .on('SUBTRACT', (state, payload) => state - payload) // Or a string representing event type

`off()`

Detaches an EventHandler from the reducer. Returns reducer.

reducer.on(double, (state) => {
  if (state > 1000) {
    reducer.off(double)
  }
  return state * 2
})

`reset()`

Attaches a special reset handler to the reducer. Reset handler always returns the initial state.

import { userLogout } from '../../someModule'
reducer.reset(userLogout)

`has()`

Checks if the reducer has a handler for provided event creator or event type.

import { userLogout } from '../../someModule'

reducer.reset(userLogout)
reducer.has(userLogout) // true

`createEvents()`

Creates an object of EventCreators from provided EventHandlers.

const { add, subtract, double } = reducer.createEvents({
  add: (state, payload) => state + payload,
  subtract: (state, payload) => state - payload,
  double: (state) => state * 2
})

createReducer