state-middleware-manager

State accumulating and reducing middleware manager

Installation

npm install state-middleware-manager

State manager types

There are 2 types of middleware manager available, depending on how you want the middleware to modify the state.

1. Accumulating state manager

State must be an object and every new state is added to the previous state.

import { accumulator } from 'state-middleware-manager'

const middleware1 = (state, next) => {
  expect(state).toEqual({})
  return next({ foo: 'bar' })
}

const middleware2 = (state, next) => {
  expect(state).toEqual({ foo: 'bar '})
  return next({ mung: 'face' })
}

accumulator([ middleware1, middleware2 ])()
  .then(state => {
    expect(state).toEqual({
      foo: 'bar',
      mung: 'face'
    })
  })

This is useful when you don't want the middleware to necessarily delete previous state, but instead, add to it.

2. State reducer manager

A little "redux"y. You pass an initial state, and always a new non-mutated property to the next function.

import { reducer } from 'state-middleware-manager'

const middleware1 = (state, next) => {
  expect(state).toEqual({ start: true })
  return next({ foo: 'bar' })
}

const middleware2 = (state, next) => {
  expect(state).toEqual({ foo: 'bar' })
  return next({ mung: 'face' })
}

accumulator([ middleware1, middleware2 ])({ start: true })
  .then(state => {
    expect(state).toEqual({ mung: 'face' })
  })

This is useful when you're happy that any middleware can change the format of the state. The state can also be any type you fancy.

Middleware

All middleware should return a promise and the next() function will return the final promise.

Examples of middleware

export async function logger (input, next) {
  console.log('--->', JSON.stringify(input))

  const output = await next()
  console.log('<---', JSON.stringify(output))
}

import { getUser } from 'my-date-store'

export async function accumulateUser (state, next) {
  if (state.userId) {
    const user = await getUser(state.userId)
    return next({ user })
  } else {
    return next()
  }
}

export async function addUser (state, next) {
  if (state.userId) {
    const user = await getUser(state.userId)
    return next({ ...state, user })
  } else {
    return next()
  }
}