create-reducer-extra

A few helpful utilities for creating boilerplate-free Redux reducers with first class support for Typescript

Installation

yarn add create-reducer-extra

Or using npm

npm install --save create-reducer-extra

Usage

As a convenience all reducing functions are called directly with the actions payload property

// actions.ts
import { action } from 'create-reducer-extra'

export const actionA = (someNumber) => ({ type: 'A', payload: someNumber })
export const actionB = (someString) => ({ type: 'B', payload: someString })
export const actionC = (someBool) => action('C', someBool)

// reducer.ts
import { createReducer } from 'create-reducer-extra'

const initialState = { counter: 0 }

export const reducer = createReducer<State, HandledActions>(initialState, {
  A: (state, payload) => ({ counter: state.counter + payload[0] }),
  B: (state, payload) => ({ counter: state.counter + Number(payload) }),
  C: (state, payload) => ({ counter: payload ? state.counter + 1 : state.counter - 1 }),
})

API

Note that all of the createReducer functions:

• Expects actions to be of the form { type: string, payload: any }
• Your your handler functions will be called directly with the payload of the action

action

A tiny utility for creating actions in the format createReducer expects

// actions.ts
import { action } from 'create-reducer-extra'

const changeName = (name) => action('ChangeName', { newName: name })

changeName('Fluffy') // { type: 'ChangeName', payload: { newName: 'Fluffy' } }

createMergeReducer

Allows you to only specify what has changed in your reducing function, e.g

import { createMergeReducer } from 'create-reducer-extra'

const initialState = {
  animals: ['ant', 'bat'],
  counter: 2,
}

const reducer = createMergeReducer(initialState, {
  Add: ({ counter }, incrementAmount) => ({ counter: counter + incrementAmount}),
  NewAnimals: ({ animals }, newAnimals) => ({ animals: [...animals, ...newAnimals] }),    
})

reducer(initialState, { payload: 5, type: 'Add' })
// { counter: 7, animals: ['ant', 'bat'] }

reducer(initialState, { payload: ['cat', 'dog'], type: 'NewAnimals' })
// { counter: 2, animals: ['ant', 'bat', 'cat', 'dog] }

createReducer

For when you want to specify exactly what the next state will be

import { createReducer } from 'create-reducer-extra'

const initialState = {
  animals: ['ant', 'bat'],
  counter: 2,
}

const reducer = createReducer(initialState, {
  Add: ({ counter }, incrementAmount) => ({ counter: counter + incrementAmount}),
  NewAnimals: ({ animals, counter }, newAnimals) => ({ animals: [...animals, ...newAnimals], counter }),    
})

reducer(initialState, { payload: 3, type: 'Add' })
// { counter: 5 }
// Note the missing 'animals' property

createResettableReducer

Provides the ability to reset a reducer to its initial state.

This can be useful for handling things such as a logout in a single page app.

The ResetState can be overridden in the handler to provide custom behaviour.

import { createResettableReducer, resetState } from 'create-reducer-extra'

const initialState = { animals: ['ant', 'bat'], counter: 2 }

const reducer = createResettableReducer(initialState, {
  Add: ({ counter }, incrementAmount) => ({ counter: counter + incrementAmount}),
  NewAnimals: ({ animals }, newAnimals) => ({ animals: [...animals, ...newAnimals] }),    
})

const nextState = reducer(initialState, { payload: 5, type: 'Add' })
// { counter: 7, animals: ['ant', 'bat'] }

reducer(nextState, resetState())
// { animals: ['ant', 'bat'], counter: 2 } === initialState

createResetMergeReducer

Combines the functionality of createMergeReducer and createResettableReducer.

Note that if the ResetState action is handled by the reducer, the result returned will be merged into the current state e.g.

import { createResetMergeReducer, resetState } from 'create-reducer-extra'

const initialState = { animals: ['ant', 'bat'], counter: 2 }

const reducer = createResetMergeReducer(initialState, {
  Add: ({ counter }, incrementAmount) => ({ counter: counter + incrementAmount}),
  [ResetState]: ({ animals }) => ({ animals: [] }),    
})

const nextState = reducer(initialState, resetState())
// { counter: 2, animals: [] }

Usage with Typescript

This library leverages some new features introduced in Typescript 2.8 to provide complete type safety with minimal boilerplate. To take advantage of completely type-safe reducers you need to:

1. Define your action creators

// actions.ts
import { action, Action } from 'create-reducer-extra'

const actionA = (param: Array<number>): Action<'A', Array<number>> =>
  ({ type: 'A', payload: param })

const actionB = (param: string): Action<'B', string> => ({ type: 'B', payload: param })

const actionC = () => action('C', false)

2. In your reducer create:

• A type to represent the state of the reducer
• A type to represent the actions your reducer should handled

3. Provide those as type parameters to your reducer-creator of choice:

// reducer.ts
import { createReducer } from 'create-reducer-extra'
import * as actions from './actions'

type State = { counter: number }
type HandledActions = typeof actions

const reducer = createReducer<State, HandledActions>(initialState, {
  A: (state, payload) => ({ counter: state.counter + payload[0] }),
  B: (state, payload) => ({ counter: state.counter + Number(payload) }),
  C: (state, payload) => ({ counter: payload ? state.counter + 1 : state.counter - 1 }),
})

Voila, everything is type-safe!