support for asynchronous actions

i keep getting the following error for async actions

action with type undefined did not modify the data in any reducer.You may have mutated state directly or you may have a typo in your reducer

i think this is because of the following code in the middleware.

const prevState = getState();
const result = next(action);
const nextState = getState();

Since the action here is a function which returns a promise we need to compare the nextState with the prevState only after the promise has been resolved. Something like the following might fix the issue

const prevState = getState();
const result = Promise.resolve(next(action));
result.then(() => {
    const nextState = getState();
    if (prevState === nextState) {
        callback(action);
    }
});

return result;

The above issue will only happen if thunk middleware is added after the redux-unhandled-action middleware. Something like the following

applyMiddleware(reduxUnhandledAction(), thunk)

But if we add thunk at the beginning, then this issue will not happen as the async action will not be forwarded to the other middlewares. So the following will work fine

applyMiddleware(thunk, reduxUnhandledAction())

So I am not sure if there is need to fix it. If this is the expected behavior, then the issue can be closed.

[conorhastings]

@oyeanuj should be position agnostic now

[oyeanuj]

@conorhastings @amit1911 So, is the middleware position agnostic? Or does it come at the end?