Function stateExtension

test/typescript/enhancers.ts:49–92

* Store enhancer that extends the type of the state.

()

 * Store enhancer that extends the type of the state.
 */
function stateExtension() {
  interface ExtraState {
    extraField: string
  }

  const enhancer: StoreEnhancer<{}, ExtraState> =
    createStore =>
    <S, A extends Action, PreloadedState>(
      reducer: Reducer<S, A, PreloadedState>,
      preloadedState?: PreloadedState | undefined
    ) => {
      function wrapReducer<PreloadedStateToWrap>(
        reducer: Reducer<S, A, PreloadedStateToWrap>
      ): Reducer<S & ExtraState, A, PreloadedStateToWrap & ExtraState> {
        return (state, action) => {
          const newState = reducer(state, action)
          return {
            ...newState,
            extraField: class="st">'extra'
          }
        }
      }
      const wrappedPreloadedState = preloadedState
        ? {
            ...preloadedState,
            extraField: class="st">'extra'
          }
        : undefined
      const store = createStore(wrapReducer(reducer), wrappedPreloadedState)
      return {
        ...store,
        replaceReducer(nextReducer: Reducer<S, A>) {
          store.replaceReducer(wrapReducer(nextReducer))
        }
      }
    }

  const store = createStore(reducer, enhancer)

  store.getState().someField
  store.getState().extraField
  class="cm">// @ts-expect-error
  store.getState().wrongField
}

/**
 * Store enhancer that adds methods to the store.