Subscriptions

🛠 Expand reducer progressively

Define subscription map in the same file scope where defined state. It looks like a mutations but does not generate an ActionType / ActionCreator. Unit subscription is equivalent to prior reducer sorted by conventional switch statement.

The subscription first argument take state of file scope. The method name and the payload schema have already been determined. Because, subscription follow origin what you defined. The only remaining work is to define change the state.

const TodosState = {
  date: new Date(),
  shouldUpdateDate: true,
  messegaFromTimer: 'no message available'
}
// ______________________________________________________
//
// @ Subscriptions

export const TodosSubscriptions = {
  Timer: {
    // Function name and payload already been determined.
    tick(state, date) {
      if (!state.shouldUpdateDate) return state
      return { ...state, date }
    },
    // Function name and payload already been determined.
    notifyMessage(state, { message }) {
      return { ...state, messegaFromTimer: message }
    }
  }
}

Timer ActionSources defined as follows.

// ______________________________________________________
//
// @ ActionSources

function tick() {
  return new Date()
}
function notifyMessage(message = 'start tick') {
  return { message }
}
export const ActionSources = {
  tick,
  notifyMessage
}

Mutations are usually sufficient,This is useful when you start to be interested outside Action. It is also possible to subscribe between aggregation and aggregation.

Related: subscribe ->