Out-of-the-box, Redux is synchronous. If you try to dispatch an async function, you'll get an error:

Actions must be plain objects. Use custom middleware for async actions.

importthunk from 'redux-thunk'
import createLogger from 'redux-logger'
const middleware = [thunk]
if (process.env.NODE_ENV !== 'production') {
 middleware.push(createLogger())
}
const store = createStore(reducers, applyMiddleware(...middleware))

redux-thunk is  middleware that will allow us to dispatch a function and wait for the result; then we can dispatch another action(s).

Here's how we can use async actions:

export const track = filter => {
   return dispatch => {
       Meteor.call('track_phrase', filter.phrase, err => {
           if (!err) {
               dispatch(selectFilter(filter.id));
          }
           //do something if you have an error. you can dispatch another action
       })
   }
}

In the action, we call a standard Meteor method by passing a filter phrase to the server...