Meta Pattern

When developing with Redux, often times we spend time on a lot of boilerplate code, and some common logic tend to become repeated. We can use Meta pattern to avoid code repetition while still taking advantage of Redux features. It is a simple concept and works like this:

In actions we define the actual type in meta property with name and type fields instead of type property. So a action looks like so:

{
  meta: {
    // Use logic/flow of this action
    type: STATIC_TYPE_NAME
    // Name of the field in the reducer so we can obtain/preserve the state of the action
    name: IDENTIFIER
  }
  // Usually it is a combination of STATIC_TYPE_NAME and IDENTIFIER for DevTools/verbosity purposes only
  type: DYNAMIC_TYPE_NAME
}

For example, we have a some logic to call API that requests for exchange rate and user profile. It would be cumbersome to write REQUEST_INIT, REQUEST_SUCCESS, REQUEST_FAILURE everytime we have a distinct API call. Normally, it would look something like this:

For some API call to get exchange rate
  // create exchangeRateReducer (INIT, SUCCESS, FAILURE)
  // create exchangeRateActions (INIT, SUCCESS, FAILURE)
  // create exchangeRateActionsCreators (INIT, SUCCESS, FAILURE)
For some API call to get user profile
  // create userReducer (INIT, SUCCESS, FAILURE)
  // create userActions (INIT, SUCCESS, FAILURE)
  // create userActionsCreators (INIT, SUCCESS, FAILURE)

... tens of other API calls with same structure

Instead, by applying meta pattern we can do this:

Initialize apiRequester reducer/actions/action creators
  // create apiRequesterReducer (INIT, SUCCESS, FAILURE)
  // create apiRequesterActions (INIT, SUCCESS, FAILURE)
  // create apiRequesterActionsCreators (INIT, SUCCESS, FAILURE)

And so then we can reuse the logic by dispatching these actions:

// Dispatch action to get exchange rate

{
  meta: {
    type: REQUEST_INIT
    name: EXCHANGE_RATE
  }
  type: EXCHANGE_RATE_REQUEST_INIT // Auto generated
}

// Dispatch action to get user profile

{
  meta: {
    type: REQUEST_INIT
    name: USER_PROFILE
  }
  type: USER_PROFILE_REQUEST_INIT // Auto generated
}

Then if we want to do something after the API calls were successful, using redux-saga or some listener we can do this:

take(USER_PROFILE_REQUEST_INIT, doSomethingWithProfileSaga)
take(EXCHANGE_RATE_REQUEST_INIT, doSomethingWithExchangeRateSaga)

Benefits are two-folds:

We can reuse the reducer/action/saga logic
In DevTools we get to see the action type with name of the request

traverse/meta_pattern.md

Meta Pattern