Create reducer with default setPayload

create-reducer.js

import { setPayload } from './setPayload';

/**
 * Busca si el handler dado es una funcion,
 * si lo es devuelve la función, si no lo es
 * devuelve una función setPayload por defecto
 * @param {function | string} actionHandler
 * @returns {function}
 * @private
 */
const _getUpdatedStateFunction = actionHandler => (
  typeof actionHandler === 'function'
    ? actionHandler
    : setPayload
);

/**
 * Comprueba si existe el action handler, si no existe devuelve
 * el estado sin modificar, si existe devuelve el estado modificado
 * por el handler
 * @param {Object} oldState
 * @param {Object} action
 * @param {Function | string} actionHandler
 * @returns {Object}
 * @private
 */
const _getNewState = (oldState, action, actionHandler) => (
  actionHandler
    ? _getUpdatedStateFunction(actionHandler)(oldState, action)
    : oldState
);

/**
 * Create reducer with the new style from {key: value}
 * @param {Object} INITIAL_STATE
 * @param {Object} ACTION_HANDLERS - typical switch
 * @returns {function(Object, Object): Object}
 */
export const createReducer = (INITIAL_STATE, ACTION_HANDLERS) => (
  (state = INITIAL_STATE, action) => (
    _getNewState(state, action, ACTION_HANDLERS[action.type])
  )
);

reducer.js

import { createReducer } from 'store/utils';
import {
  MY_ACTION2
} from './types';

const INITIAL_STATE = {
  myState: null,
};

const ACTION_HANDLERS = {
  MY_ACTION,
  MY_ACTION2: () => INITIAL_STATE,
};

export default createReducer(INITIAL_STATE, ACTION_HANDLERS);

setPayload.js

/**
 * Devuelve un estado con los cambios del payload dado
 * @param state
 * @param payload
 */
export const setPayload = (state, { payload }) => ({ ...state, ...payload });