npm install redux-thunk

yarn add redux-thunk

- const ReduxThunk = require('redux-thunk')
+ const ReduxThunk = require('redux-thunk').default

import ReduxThunk from 'redux-thunk'; // no changes here 😀

const ReduxThunk = window.ReduxThunk.default;

const INCREMENT_COUNTER = 'INCREMENT_COUNTER';

function increment() {
  return {
    type: INCREMENT_COUNTER,
  };
}

function incrementAsync() {
  return (dispatch) => {
    setTimeout(() => {
      // Yay! Can invoke sync or async actions with `dispatch`
      dispatch(increment());
    }, 1000);
  };
}

function incrementIfOdd() {
  return (dispatch, getState) => {
    const { counter } = getState();

    if (counter % 2 === 0) {
      return;
    }

    dispatch(increment());
  };
}

// calculation of 1 + 2 is immediate
// x === 3
let x = 1 + 2;

// calculation of 1 + 2 is delayed
// foo can be called later to perform the calculation
// foo is a thunk!
let foo = () => 1 + 2;

npm install redux-thunk

import { createStore, applyMiddleware } from 'redux';
import thunk from 'redux-thunk';
import rootReducer from './reducers/index';

// Note: this API requires redux@>=3.1.0
const store = createStore(rootReducer, applyMiddleware(thunk));

import { createStore, applyMiddleware } from 'redux';
import thunk from 'redux-thunk';
import rootReducer from './reducers';

// Note: this API requires redux@>=3.1.0
const store = createStore(rootReducer, applyMiddleware(thunk));

function fetchSecretSauce() {
  return fetch('https://www.google.com/search?q=secret+sauce');
}

// These are the normal action creators you have seen so far.
// The actions they return can be dispatched without any middleware.
// However, they only express “facts” and not the “async flow”.

function makeASandwich(forPerson, secretSauce) {
  return {
    type: 'MAKE_SANDWICH',
    forPerson,
    secretSauce,
  };
}

function apologize(fromPerson, toPerson, error) {
  return {
    type: 'APOLOGIZE',
    fromPerson,
    toPerson,
    error,
  };
}

function withdrawMoney(amount) {
  return {
    type: 'WITHDRAW',
    amount,
  };
}

// Even without middleware, you can dispatch an action:
store.dispatch(withdrawMoney(100));

// But what do you do when you need to start an asynchronous action,
// such as an API call, or a router transition?

// Meet thunks.
// A thunk in this context is a function that can be dispatched to perform async
// activity and can dispatch actions and read state.
// This is an action creator that returns a thunk:
function makeASandwichWithSecretSauce(forPerson) {
  // We can invert control here by returning a function - the "thunk".
  // When this function is passed to `dispatch`, the thunk middleware will intercept it,
  // and call it with `dispatch` and `getState` as arguments.
  // This gives the thunk function the ability to run some logic, and still interact with the store.
  return function(dispatch) {
    return fetchSecretSauce().then(
      (sauce) => dispatch(makeASandwich(forPerson, sauce)),
      (error) => dispatch(apologize('The Sandwich Shop', forPerson, error)),
    );
  };
}

// Thunk middleware lets me dispatch thunk async actions
// as if they were actions!

store.dispatch(makeASandwichWithSecretSauce('Me'));

// It even takes care to return the thunk’s return value
// from the dispatch, so I can chain Promises as long as I return them.

store.dispatch(makeASandwichWithSecretSauce('My partner')).then(() => {
  console.log('Done!');
});

// In fact I can write action creators that dispatch
// actions and async actions from other action creators,
// and I can build my control flow with Promises.

function makeSandwichesForEverybody() {
  return function(dispatch, getState) {
    if (!getState().sandwiches.isShopOpen) {
      // You don’t have to return Promises, but it’s a handy convention
      // so the caller can always call .then() on async dispatch result.

      return Promise.resolve();
    }

    // We can dispatch both plain object actions and other thunks,
    // which lets us compose the asynchronous actions in a single flow.

    return dispatch(makeASandwichWithSecretSauce('My Grandma'))
      .then(() =>
        Promise.all([
          dispatch(makeASandwichWithSecretSauce('Me')),
          dispatch(makeASandwichWithSecretSauce('My wife')),
        ]),
      )
      .then(() => dispatch(makeASandwichWithSecretSauce('Our kids')))
      .then(() =>
        dispatch(
          getState().myMoney > 42
            ? withdrawMoney(42)
            : apologize('Me', 'The Sandwich Shop'),
        ),
      );
  };
}

// This is very useful for server side rendering, because I can wait
// until data is available, then synchronously render the app.

store
  .dispatch(makeSandwichesForEverybody())
  .then(() =>
    response.send(ReactDOMServer.renderToString(<MyApp store={store} />)),
  );

// I can also dispatch a thunk async action from a component
// any time its props change to load the missing data.

import { connect } from 'react-redux';
import { Component } from 'react';

class SandwichShop extends Component {
  componentDidMount() {
    this.props.dispatch(makeASandwichWithSecretSauce(this.props.forPerson));
  }

  componentDidUpdate(prevProps) {
    if (prevProps.forPerson !== this.props.forPerson) {
      this.props.dispatch(makeASandwichWithSecretSauce(this.props.forPerson));
    }
  }

  render() {
    return <p>{this.props.sandwiches.join('mustard')}</p>;
  }
}

export default connect((state) => ({
  sandwiches: state.sandwiches,
}))(SandwichShop);

const store = createStore(
  reducer,
  applyMiddleware(thunk.withExtraArgument(api)),
);

// later
function fetchUser(id) {
  return (dispatch, getState, api) => {
    // you can use api here
  };
}

const api = "http://www.example.com/sandwiches/";
const whatever = 42;

const store = createStore(
  reducer,
  applyMiddleware(thunk.withExtraArgument({ api, whatever })),
);

// later
function fetchUser(id) {
  return (dispatch, getState, { api, whatever }) => {
    // you can use api and something else here
  };
}