Thunk Middleware with Custom API Utils

action.js

// Now your action creators can pull utilities our of their thunk api!
export function fetchUser(id) {
  return ({api, dispatch}) =>
    api.fetch(`users/${id}`).then(resp =>
      dispatch({action: FETCH_USER, user: resp.body.data}));
}

action.test.js

// And now testing is *super* easy - just inject away!
it ('should hit correct endpoint', () => {
  const api = createMockApi([
    {test: 'users/1', resp: ({data: {id: 1, type: 'user', name: 'Chris'}})}
  ]);
  const store = createMockAppStore({api});
  
  store.dispatch(fetchUser(1));
  
  expect(api.fetch.firstCall.args[0]).toEqual('users/1');
  expect(store.dispatch.firstCall.args[0]).toEqual(
    {action: FETCH_USER, user: {id: 1, type: 'user', name: 'Chris'}}
  );
})

app.js

// setup middleware with whatever we want to inject via a thunk args interface
const args = {};
const thunkMiddleware = createThunkMiddleware(args);
args.api = api;
args.getState = store.getState;
args.dispatch = store.dispatch;

thunk-middlware.js

// Where the magic happens
export function createThunkMiddleware(args) {
  return function createDispatch(next) {
    return function doDispatch(action) {
      if (isFunction(action)) {
        return doDispatch(action(args));
      }
      
      return next(action);
    }
  }
}