Dispatch in middleware does not use store-enhancer dispatch

[dpwrussell]

Hi,

I am experimenting with this:

Your custom middleware can intercept this action to dispatch new actions in response to URL changes.

I have written a barebones middleware for routes with auth in their result. Like so:

export const auth = store => next => action => {

  if (
    action.type === LOCATION_CHANGED &&
    action.payload &&
    action.payload.result &&
    action.payload.result.auth
  ) {

    const loggedIn = selectors.isLoggedIn(store.getState());

    if (!loggedIn) {
      setTimeout(() => {
        store.dispatch({
          type: PUSH,
          payload: '/login'
        });
        // Other dispatch which works perfectly
        // store.dispatch(fetchVocabsIfNeeded());
      }, 3000);
    }
  }
  return next(action);
};

The setTimeout is just to simulate an async fetch that I would usually dispatch to the server to see if I had an active session. If not, then I want to go to the login page.

This seems to generate a ROUTER_PUSH action with a payload of '/login'. The route does not change and a fragment for '/login' is not displayed. However, if I dispatch that same action from an onClick on my App component, the result is a ROUTER_LOCATION_CHANGE with the payload of pathname, key, route, params, etc, and it works fine.

I am not experienced with redux middleware and suspect that this has something to do with the middleware chain and where redux-little-router sits in that chain, but I'm unsure how to address this. Should this be possible?

Cheers

[dpwrussell]

I created my store like so:

export default function configureStore(initialState = undefined) {
  const enhancer = compose(

    createStoreWithRouter({
      routes,
      pathname: location.pathname,
      basename: ''
    }),

    // Middleware
    applyMiddleware(
      thunkMiddleware,
      auth
    ),

    DevTools.instrument()
  );

  const store = createStore(
    reducers,
    initialState,
    enhancer
  );

[dpwrussell]

Ok, I dug a little more. The problem is that the store.dispatch in the middleware does not use the store enhancer's dispatch function. So actions dispatched in middleware will go direct to the store's dispatchmethod which explains why it works for other things, but not PUSH etc. react-little-router's enhancer would have intercepted PUSH if it was in the chain.

[tptee]

Thanks for reporting this! I'll be investigating this tomorrow 👍

[dpwrussell]

Actually, it's even worse than I thought. Middleware should always be the first enhancer and I jsut realised that when fiddling around to get it to work the above is the wrong order.

With the correct order of applyMiddleware then createStoreWithRouter, the middleware will never receive LOCATION_CHANGED events at all.

The fix for this isn't that complicated, but it is a bit messy. I've been having a look at the redux documentation and while it doesn't say that you shouldn't dispatch actions from within an enhancer, I'm beginning to think it isn't a good idea because unlike the middleware, it does not start again from the beginning of the chain.

The only way I could fix this was to split redux-little-router into two parts. I now have a middleware and a store enhancer. This also meant that I configured the history, basename and matcher in my configureStore function as these are passed into both the middleware and enhancer.

Because middleware is designed with this exact problem in mind, it works. If you are interested in this solution I am happy to write it up or submit a PR.

[tptee]

Middleware should always be the first enhancer

Not always true (wish it were that easy!). See where redux-loop ran into this same issue:
redux-loop/redux-loop#28
redux-loop/redux-loop#39

This issue appears to be a pretty serious (and intentional) limitation of Redux:
reduxjs/redux#1240
reduxjs/redux#1051

...which really puts library authors in a tight spot. Older versions of this library required you to install both a store enhancer and a middleware, which definitely hurts usability and expands boilerplate.

Going to hack on a solution as soon as I can, would love feedback when I have something ready!

[tptee]

Also had a thought: in your example, can you try calling next instead of store.dispatch just to see what happens?

[tptee]

I can't figure this out for the life of me! 😒 The only solution I know of is to reintroduce the routerMiddleware, but as an optional piece to allow dispatching router events in middleware.

[caesarsol]

Hello, I don't know if this makes sense, bit I would use something else to dispatch a second action when receiving a first one, and that's a Saga from redux-saga (or maybe something from redux-loop if I understand that project correctly).

So my question is: are you sure this is a redux-little-router problem?

(Still I'm curious too if using next() instead of dispatch() in @dpwrussell 's code could work. @tptee which one do you use from your enhancer?)

[dpwrussell]

@tptee Hi, I finally made time to go and do the investigation you asked for.

Doing next instead of store.dispatch does not work. I wasn't really expecting it to, because the order that the enhancers are dispatched is left-to-right as they are in the compose statement.

I double checked this by adding this enhancer:

const testEnhancer = createStore => (reducer, preloadedState, enhancer) => {

  const store = createStore(reducer, preloadedState, enhancer);

  const dispatch = action => {
    console.log('testEnhancer dispatch', action);
    return store.dispatch(action);
  }

  return { ...store, dispatch };
};

Which is composed like so:

  const enhancer = compose(

    routerEnhancer,

    applyMiddleware(
      thunkMiddleware,
      auth
    ),

    testEnhancer,

    // Browser addon redux tools (develop mode only)
    window.devToolsExtension ? window.devToolsExtension() : f => f
  );

As expected, testEnhancer logs the next(action) call that I make from my middleware. If the testEnhancer is moved before applyMiddleware in the composition, then it is not.

It is my belief that actions should only be dispatched from middleware.

[philipyoungg]

The problem happens because with dispatch an action in store enhancer. It didn't follow the apply middleware generated dispatch action.

We can fix this by separating it to two parts: middleware and store enhancer.

Adding the dispatch 'ROUTER_PUSH' to part of middleware should've fixed the problem.