Why redux-loop actions skip all middlewares?

Question

I run redux-loop official example with a little change:

1. Instead of fetch I use promise with a timeout.
2. I added log middleware (copy-paste from redux.js.org tutorial).

side-effect function:

import {createStore, compose, applyMiddleware} from 'redux';
import {install, loop, Cmd} from 'redux-loop';

function fetchUser(userId) {
    return Promise.resolve((res, rej) => setTimeout(() => res(userId), 1000));
}

Actions:

function initAction() {
    return {
        type: 'INIT'
    };
}

function userFetchSuccessfulAction(user) {
    return {
        type: 'USER_FETCH_SUCCESSFUL',
        user
    };
}

function userFetchFailedAction(err) {
    return {
        type: 'USER_FETCH_ERROR',
        err
    };
}

Initial state:

const initialState = {
        initStarted: false,
        user: null,
        error: null
    };

Reducer:

function reducer(state = initialState, action) {
        console.log(action);  // I added this line
        switch (action.type) {
            case 'INIT':
                return loop(
                    {...state, initStarted: true},
                    Cmd.run(fetchUser, {
                        successActionCreator: userFetchSuccessfulAction,
                        failActionCreator: userFetchFailedAction,
                        args: ['1234']
                    })
                );

            case 'USER_FETCH_SUCCESSFUL':
                return {...state, user: action.user};

            case 'USER_FETCH_FAILED':
                return {...state, error: action.error};

            default:
                return state;
        }
    }

My custom log middleware:

    const logger = store => next => action => {
        console.group(action.type);
        console.info('dispatching', action);
        let result = next(action);
        console.log('next state', store.getState());
        console.groupEnd();
        return result
    };

Configure store:

const enhancer = compose(
        applyMiddleware(logger),
        install()
    );

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

Dispatching the first action to start it all: (my code)

store.dispatch(initAction());

output:

---

As you can see, the second action skipped my log middleware and also the last line of the log is not clear to me. Why the reducer received a function instead of the actual user object?

Answer 1

Why the reducer received a function instead of the actual user object?

return Promise.resolve((res, rej) => setTimeout(() => res(userId), 1000));

Promise.resolve is used to create a promise already in the resolved state. It expects you to pass in what value the promise should resolve with, and in your case, you've asked it to resolve to a function.

You probably meant to do:

return new Promise((res, rej) => setTimeout(() => res(userId), 1000))