Question about middlewareAPI

[ccniuj]

In applyMiddleware.js:

export default function applyMiddleware(...middlewares) {
  return (createStore) => (reducer, preloadedState, enhancer) => {
    var store = createStore(reducer, preloadedState, enhancer)
    var dispatch = store.dispatch
    var chain = []

    var middlewareAPI = {
      getState: store.getState,
      dispatch: (action) => dispatch(action)
    }
    chain = middlewares.map(middleware => middleware(middlewareAPI))
    dispatch = compose(...chain)(store.dispatch)

    return {
      ...store,
      dispatch
    }
  }
}

I think we can simply pass dispatch instead of wrapping it in a lambda:

export default function applyMiddleware(...middlewares) {
  return (createStore) => (reducer, preloadedState, enhancer) => {
    var store = createStore(reducer, preloadedState, enhancer)
    var dispatch = store.dispatch
    var chain = []

    var middlewareAPI = {
      getState: store.getState,
      dispatch
    }
    chain = middlewares.map(middleware => middleware(middlewareAPI))
    dispatch = compose(...chain)(store.dispatch)

    return {
      ...store,
      dispatch
    }
  }
}

The code above passes all the tests except for this one:

applyMiddleware › passes recursive dispatches through the middleware chain
expect(received).toEqual(expected)
Expected value to equal:
  2
Received:
  1

So here's my question: Is there any specific concern about the original version of middlewareAPI? Or is it okay to improve it?

[jimbolla]

Here's the commit where that was added: af474ba. Unsure why. Is the current implementation causing you problems?

[ccniuj]

@jimbolla
Thanks for your reply. This is not really causing any problem but just making me wonder is there any insight behind the current implementation.

[sunkai612]

@davidjuin0519
Not sure if "to only compose dispatch method once" is the reason for that lambda.

[markerikson]

This has been asked in previous issues. I don't have a link to the specific official answer at the moment, but I believe it's to set up a closure referring to the original dispatch function.

[ccniuj]

@markerikson
Thanks for your reply. I think I found the discussion #1592 which reveals that the purpose of using a closure is to bind dispatch dynamically. 😀