Redux middleware to make store.dispatch() return a promise and wait for another action.
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README.md

Redux Wait for Action

Build Status npm version

Redux middleware to make store.dispatch() return a promise which will be fulfilled when another specified action is dispatched, which is useful for universal(isomorphic) React Web Apps with redux and server-side rendering.

npm install --save redux-wait-for-action

Quick Start

Minimal starter kit for universal apps with redux and redux-saga

Basic Usage

To fire todos/get action and subscribe for todos/get/success action:

import { WAIT_FOR_ACTION, ERROR_ACTION } from 'redux-wait-for-action';
store.dispatch({
  type: 'todos/get',
  [ WAIT_FOR_ACTION ]: 'todos/get/success', // Specify which action we are waiting for
  [ ERROR_ACTION ]: 'todos/get/failed', // Optional
}).then( payload => console.log('Todos got!') )
.catch( error => console.error('Failed!' + error.message) );

Alternatively, use conditional functions as WAIT_FOR_ACTION, which is useful when firing multiple actions with same action.type in parallel:

store.dispatch({
  type: 'profile/get',
  [ WAIT_FOR_ACTION ]: action => action.type === 'profile/get/success' && action.id === 1,
  // Only subscribe for profile/get/success action whose profile id equals 1
  [ ERROR_ACTION ]: action => action.type === 'profile/get/failed' && action.id === 1,
}).then( payload => console.log('ID #1 Profile got!') )
.catch( error => console.error('Failed!' + error.message) );

For Isomorphic Apps

  • For each React container, we define a static function fetchData() where we return a store.dispatch() call followed by automatic execution of side effects. We should call this store.dispatch() with an action that also contains information about which action we are waiting for.
  • Use those fetchData()s to populate page data on both client and server side.
  • On server side, we put the rendering logic in fetchData().then(() => { /* rendering logic here! */ }), where side effects are completed and an action with finishing flag is dispatched.
  • If you are using redux-thunk, store.dispatch() already returns a promise and you probably don't need this middleware. However, side effects like redux-saga running separately from primitive Redux flow don't explicitly notify us when a specific async fetch is finished, in which case redux-wait-for-action does the trick and makes those async tasks subscribable.
  • Although redux-saga added runSaga().done support which returns a promise to tell when a specific saga task is completed, it's quite tricky where saga tasks aren't started by a dispatch() call and it does't work when using sagas containing infinite loops.

Usage with react-router and redux-saga

configureStore() function where a Redux store is created on both client and server side:

import createReduxWaitForMiddleware from 'redux-wait-for-action';

function configureStore(initialState) {
  const sagaMiddleware = createSagaMiddleware();
  let enhancer = compose(
    applyMiddleware(sagaMiddleware),
    applyMiddleware(createReduxWaitForMiddleware()),
  );
  const store = createStore(rootReducer, initialState, enhancer);

  // ...
}

Assume we have saga effects like this:

function* getTodosSaga() {
  const payload = yield call(APIService.getTodos);
  yield put({
    type: 'todos/get/success',
    payload
  });
}
function* rootSaga() {
  yield takeLatest('todos/get', getTodosSaga);
}

Define a fetchData() for each of our containers:

import { WAIT_FOR_ACTION } from 'redux-wait-for-action';

class TodosContainer extends Component {
  static fetchData(dispatch) {
    return dispatch({
      type: 'todos/get',
      [ WAIT_FOR_ACTION ]: 'todos/get/success',
    });
  }
  componentDidMount() {
    // Populate page data on client side
    TodosContainer.fetchData(this.props.dispatch);
  }
  // ...
}

Here in our action we specify WAIT_FOR_ACTION as 'profile/get/success', which tells our promise to wait for another action 'profile/get/success'. WAIT_FOR_ACTION is a ES6 Symbol instance rather than a string, so feel free using it and it won't contaminate your action.

Next for server side rendering, we reuse those fetchData()s to get the data we need:

//handler for Express.js
app.use('*', handleRequest);
function handleRequest(req, res, next) {
  //...
  match({history, routes, location: req.url}, (error, redirectLocation, renderProps) => {
    //...handlers for redirection, error and null renderProps...

    const getReduxPromise = () => {
      const component = renderProps.components[renderProps.components.length - 1].WrappedComponent;
      const promise = component.fetchData ?
        component.fetchData(store.dispatch) :
        Promise.resolve();
      return promise;
    };

    getReduxPromise().then(() => {
      const initStateString = JSON.stringify(store.getState());
      const html = ReactDOMServer.renderToString(
        <Provider store={store}>
          { <RouterContext {...renderProps}/> }
        </Provider>
      );
      res.status(200).send(renderFullPage(html, initStateString));
    });
  });
}

Advanced Usage

Error Handling

Use try-catch clause in saga effects. The todos/get/failed action object should contain a top-level key error or err whose value is an error descriptor(An Error() instance or a string).

function* getTodosSaga() {
  yield take('todos/get');
  try {
    const payload = yield call(APIService.getTodos);
    yield put({
      type: 'todos/get/success',
      payload
    });
  } catch (error) {
    yield put({
      type: 'todos/get/failed',
      error
    });
  }
}

Make sure both WAIT_FOR_ACTION and ERROR_ACTION symbols are specified in your todos/get action:

import { WAIT_FOR_ACTION, ERROR_ACTION } from 'redux-wait-for-action';

class TodosContainer extends Component {
  static fetchData(dispatch) {
    return dispatch({
      type: 'todos/get',
      [ WAIT_FOR_ACTION ]: 'todos/get/success',
      [ ERROR_ACTION ]: 'todos/get/failed',
    });
  }
  // ...
}

Server side rendering logic:

getReduxPromise().then(() => {
  // ...
  res.status(200).send(renderFullPage(html, initStateString));
}).catch((error) => { //action.error is passed to here
  res.status(500).send(error.message);
});