Redux enhancer example

Question

I am new to redux. I would like know how I could create my own enhancer in redux. I didn't find any example to create enhancer. To create enhancers, So what arguments do I need to pass and what do I need to return? Is there any rule on creating custom enhancer?

In redux documentation about enhancer, found below two links (no sample or example code)

• store-enhancer
• using store enhancer

Redux documentation said that,

Middleware adds extra functionality to the Redux dispatch function; enhancers add extra functionality to the Redux store. ... A middleware which logs dispatched actions and the resulting new state. An enhancer which logs the time taken for the reducers to process each action.

So, I am not sure that custom middleware and custom enhancer coding rule are the same like below

const loggerMiddleware = storeAPI => next => action => {
  console.log('dispatching', action)
  let result = next(action)
  console.log('next state', storeAPI.getState())
  return result
}

So, my question is how to create custom enhancer?

Answer 1

Here is the store enhancer interface

export type StoreEnhancer<Ext = {}, StateExt = never> = (
  next: StoreEnhancerStoreCreator<Ext, StateExt>
) => StoreEnhancerStoreCreator<Ext, StateExt>
export type StoreEnhancerStoreCreator<Ext = {}, StateExt = never> = <
  S = any,
  A extends Action = AnyAction
>(
  reducer: Reducer<S, A>,
  preloadedState?: PreloadedState<S>
) => Store<ExtendState<S, StateExt>, A, StateExt, Ext> & Ext

enhancers are high-order functions that take createStore and return a new enhanced version of createStore. Take a look at this sample implementation.

const ourAwesomeEnhancer = createStore => (reducer, initialState, enhancer) => {
  const store = createStore(monitoredReducer, initialState, enhancer);
  //  add enhancer logic

  return {
    ...store
    //   you can override the some store properties or add new ones
  };
};

There is an example in official doc:

const round = number => Math.round(number * 100) / 100

const monitorReducerEnhancer = createStore => (
  reducer,
  initialState,
  enhancer
) => {
  const monitoredReducer = (state, action) => {
    const start = performance.now()
    const newState = reducer(state, action)
    const end = performance.now()
    const diff = round(end - start)

    console.log('reducer process time:', diff)

    return newState
  }

  return createStore(monitoredReducer, initialState, enhancer)
}

export default monitorReducerEnhancer