fix(combineReducers): add comments and refactor code; trigger semanti…

…c-release

(semantic-release doesn't consider "perf" commits)

src/combineReducers.js

@@ -9,27 +9,37 @@ export default function combineReducers(reducers, createInitialState = Map) {
   const actionHandlers = {}
   const otherReducers = {}
   const initialStateObj = {}
+
+  // regroup reducers that have actionHandlers:
+  //   from: prop name -> action type -> reducer
+  //     to: action type -> prop name -> reducer
+  // put reducers without actionHandlers into a prop name -> reducer map
+
   forEach(reducers, (reducer, key) => {
     initialStateObj[key] = reducer(undefined, {})
     if (reducer.actionHandlers) {
-      // invert from prop name -> action type -> reducer
-      //          to action type -> prop name -> reducer
       forEach(reducer.actionHandlers, (actionHandler, type) => {
         (actionHandlers[type] || (actionHandlers[type] = {}))[key] = actionHandler
       })
     } else otherReducers[key] = reducer
   })
   const initialState = createInitialState(initialStateObj)
 
+  // now we can create a more efficient reducer for each action type
+  // and one more efficient reducer for the otherReducers
+
+  // creates an efficient reducer from a prop name -> reducer map
   const combineBase = reducers => {
     let result
     if (size(reducers) > 1) {
+      // we have to update multiple keys; use state.withMutations
       result = (state = initialState, action) => state.withMutations(mutableState => reduce(
         reducers,
         (nextState, reducer, key) => nextState.update(key, value => reducer(value, action)),
         mutableState)
       )
     } else {
+      // we only have to update one key; use state.update
       const key = Object.keys(reducers)[0]
       const reducer = reducers[key]
       result = (state = initialState, action) => state.update(key, value => reducer(value, action))
@@ -47,9 +57,9 @@ export default function combineReducers(reducers, createInitialState = Map) {
     : undefined
 
   if (actionHandlerReducer && otherReducer) return composeReducers(actionHandlerReducer, otherReducer)
-  else if (actionHandlerReducer) return actionHandlerReducer
-  else if (otherReducer) return otherReducer
-  else return (state = initialState) => state
+  if (actionHandlerReducer) return actionHandlerReducer
+  if (otherReducer) return otherReducer
+  return (state = initialState) => state
 }