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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);
});

Overriding the Default Promise Arguments

By default the payload or data field on the WAIT_FOR_ACTION action is provided to the promise when it is resolved, or rejected with the error or err field.

There are two additional symbols, CALLBACK_ARGUMENT and CALLBACK_ERROR_ARGUMENT, which can be used to override this behavior. If functions are stored on the action using these symbols, they will be invoked and passed the entire action. The result returned from either function is used to resolve or reject the promise based on which symbol was used.

import { WAIT_FOR_ACTION, ERROR_ACTION, CALLBACK_ARGUMENT, CALLBACK_ERROR_ARGUMENT} from 'redux-wait-for-action';
store.dispatch({
  type: 'todos/get',
  [ WAIT_FOR_ACTION ]: 'todos/get/success',
  [ ERROR_ACTION ]: 'todos/get/failed',
  [ CALLBACK_ARGUMENT ]: action => action.customData,
  [ CALLBACK_ERROR_ARGUMENT ]: action => action.customError,
}).then( customData => console.log('Custom Data: ', customData) )
.catch( customError => console.error('Custom Error: ', customError) );
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