Equivalent Code

0_actions.js

import { makeActionCreator } from 'redux-toolbelt'

export const increaseBy = makeActionCreator('INCREASE_BY')

1_reducers.js

import { makeReducer } from 'redux-toolbelt'

import { increaseBy } from 'actions'

export const countReducer = makeReducer(increaseBy,
  (state, { payload }) => state + payload,
  {defaultState: 100}
)