Function combineReducers

src/combineReducers.ts:123–201

(reducers: {
  [key: string]: Reducer<any, any, any>
})

    >
  : never
export default function combineReducers(reducers: {
  [key: string]: Reducer<any, any, any>
}) {
  const reducerKeys = Object.keys(reducers)
  const finalReducers: { [key: string]: Reducer<any, any, any> } = {}
  for (let i = 0; i < reducerKeys.length; i++) {
    const key = reducerKeys[i]

    if (process.env.NODE_ENV !== class="st">'production') {
      if (typeof reducers[key] === class="st">'undefined') {
        warning(`No reducer provided for key class="st">"${key}"`)
      }
    }

    if (typeof reducers[key] === class="st">'function') {
      finalReducers[key] = reducers[key]
    }
  }
  const finalReducerKeys = Object.keys(finalReducers)

  class="cm">// This is used to make sure we don't warn about the same
  class="cm">// keys multiple times.
  let unexpectedKeyCache: { [key: string]: true }
  if (process.env.NODE_ENV !== class="st">'production') {
    unexpectedKeyCache = {}
  }

  let shapeAssertionError: unknown
  try {
    assertReducerShape(finalReducers)
  } catch (e) {
    shapeAssertionError = e
  }

  return function combination(
    state: StateFromReducersMapObject<typeof reducers> = {},
    action: Action
  ) {
    if (shapeAssertionError) {
      throw shapeAssertionError
    }

    if (process.env.NODE_ENV !== class="st">'production') {
      const warningMessage = getUnexpectedStateShapeWarningMessage(
        state,
        finalReducers,
        action,
        unexpectedKeyCache
      )
      if (warningMessage) {
        warning(warningMessage)
      }
    }

    let hasChanged = false
    const nextState: StateFromReducersMapObject<typeof reducers> = {}
    for (let i = 0; i < finalReducerKeys.length; i++) {
      const key = finalReducerKeys[i]