switch and object lookup redux

switchReducer.js

//You can use an object as a lookup table instead


const handlers = {
  ADD_ITEM(state, action) { ... }
  REMOVE_ITEM(state, action) { ... }
}

function itemReducer (state, action) {
  if (action.type in handlers) {
    return handlers[action.type](state, action)
  } else {
    return state
  }
}
                           
// OR
 function createReducer (initialState, actionMap) {
  return function reducer (state = initialState, action) {
    if (action.type in actionMap) {
      const result = actionMap[action.type](state, action)
      if (result === undefined) {
        console.warn('Reducer returned undefined for action ' + action.type + ', ignoring')
        return state
      } else {
        return result
      }
    } else {
      return state
    }
  }
}
// Then
const itemReducer = createReducer({ items: [] }, {
  ADD_ITEM (state, action) {
    return state.items.concat(action.payload)
  },
  REMOVE_ITEM (state, action) {
    return state.items.filter(it => it === action.payload)
  }
})

// You don’t need to introduce yet another thing to hold in your head while you learn a new system.
// It also reinforces that redux is just JS. There’s no magic behind what it’s doing.
// It’s just an asynchronous version of `listOfActions.reduce(reducer, initialState)`

//There’s some sort of tradeoff there for very high-performance needs (performance >= 60fps). 
// Switch statements are somehow aggressively optimized by the VM (at least in Chrome), 
// so are nominally faster than object lookups for reasonable numbers of case clauses.