difference between return and dispatch in actions: Redux

Question

I have noticed that sometimes actions in Redux use return and others dispatch. I also noticed that dispatch is used when there is some async operation in that action function, like reading/posting from/to a database, but I don't understand why. Could anyone shed some light on the crucial difference. Why don't we use dispatch all the time for example, as in context API in React?

EDIT: I will add an example, that doesn't deal with the backend, so there is no async await cycle:

 //with return
    export const addLog = (log) => {
       return{
         type: ADD_LOG,
         payload: log
       }
    }
    //with dispatch
    export const addLog = (log) => disptach => {
       dispatch{
         type: ADD_LOG,
         payload: log
       }
    }

What's the difference between the two?

Answer 1

I am quite surprised nobody has come up with a definite answer. This comes really late but I will post this for people having the same question using redux-thunk as an example. As per the docs:

there is just one important thing you need to know: by using this specific middleware, an action creator can return a function instead of an action object. This way, the action creator becomes a thunk

The function returned receives the dispatch method as an argument, which you should use to trigger state updates, since the function by itself cannot dispatch actions event if you return an object. For example:

const getEvents = () => {
  return async (dispatch) => {
    const res = await fetch(
        'https://someendpoint/events'
    );
    const events = await res.json();

    return { // <-- this will NOT be sent to any reducer
        type: GET_EVENTS,
        events: [],
    };

   dispatch({ // <-- this will 
        type: GET_EVENTS,
        events,
    });
 };

};

The section on Async Action creators explains this in more detail.