reducer-polymorphic.js

import {setEntries, next, vote, INITIAL_STATE} from './core';

// This is a polymorphic aprorach that conforms to all SOLID principles
// This reduce is much simpler and will raise an error if the action does not exist
export default function reducer(state = INITIAL_STATE, action) {
  return action.handler(state, action.payload);
}

// This is the defensive version of the reducer above, if there is an error returns the current state
export default function maybeReducer(state = INITIAL_STATE, action) {
  try {
    return reducer(state, action);
  } catch (err) {
    console.warn(err);
    return state;
  }
}
// you can stack actions the same way with the benefit that a typo on the action function will raise an error
const actions = [
    {handler: setEntries, payload: ['Trainspotting', '28 Days Later']},
    {handler: next},
    {handler: vote, payload: 'Trainspotting'},
    {handler: vote, payload: '28 Days Later'},
    {handler: vote, payload: 'Trainspotting'},
    {handler: next}
];

// this returns the same think as the reducer-standard.js but raises an error if something goes worng
const finalState = actions.reduce(reducer, Map());

// this returns the same think as above but swallow errors
const finalState2 = actions.reduce(maybeReducer, Map());

// allows you to create a action on the fly, without modifying the reducer
const finalState3 = reducer(finalState, {handler: (state => state.set('isNice', true) });

// Example of a store dispatch
store.dispatch({handler: vote, payload: 'Trainspotting'});

reducer-standard.js

import {setEntries, next, vote, INITIAL_STATE} from './core';

// This is kind of the standard aproach 
// it violates the open closed and single resposability priciplse by having a huge while loop that knows about all available actions
// Also it is hard to create variations of this reducer without duplicationt a lot of code, 
// the more actions you have the bigger this function becomes (open closed violation). 
export default function reducer(state = INITIAL_STATE, action) {
  switch (action.type) {
  case 'SET_ENTRIES':
    return setEntries(state, action.payload);
  case 'NEXT':
    return next(state);
  case 'VOTE':
    return vote(state, action.payload)
  }
  
  // this will swallow errors if the action you try to use dont exist
  return state;
}

// this is how people use it for stacking changes
  const actions = [
    {type: 'SET_ENTRIES', payload: ['Trainspotting', '28 Days Later']},
    {type: 'NEXT'},
    {type: 'VOTE', payload: 'Trainspotting'},
    {type: 'VOTE', payload: '28 Days Later'},
    {type: 'VOTE', payload: 'Trainspotting'},
    {type: 'NEXT'}
  ];
  
  const finalState = actions.reduce(reducer, Map());