CODEWITHSUNDEEP
reduxngrxngrx-effects
balteo
balteo

Reputation: 24679

Handling errors/failures in ngrx/redux reducer functions

My question relates to redux and more specifically how to handle errors/failures from within reducer functions. I am in reference to the ngrx example app (https://github.com/ngrx/example-app) and the way it handle errors/failures.

Here is the reducer function I am referring to:

export function reducer(state = initialState, action: collection.Actions): State {
  switch (action.type) {
    case collection.ActionTypes.LOAD: {
      return Object.assign({}, state, {
        loading: true
      });
    }

    case collection.ActionTypes.LOAD_SUCCESS: {
      const books = action.payload;

      return {
        loaded: true,
        loading: false,
        ids: books.map(book => book.id)
      };
    }

    case collection.ActionTypes.ADD_BOOK_SUCCESS:
    case collection.ActionTypes.REMOVE_BOOK_FAIL: {
      const book = action.payload;

      if (state.ids.indexOf(book.id) > -1) {
        return state;
      }

      return Object.assign({}, state, {
        ids: [ ...state.ids, book.id ]
      });
    }

    case collection.ActionTypes.REMOVE_BOOK_SUCCESS:
    case collection.ActionTypes.ADD_BOOK_FAIL: {
      const book = action.payload;

      return Object.assign({}, state, {
        ids: state.ids.filter(id => id !== book.id)
      });
    }

    default: {
      return state;
    }
  }
}

Can someone please explain the necessity for dealing with those two actions from within the reducer function:

For instance why remove the book from the state (in the case of the ADD_BOOK_FAIL action)?

If the add book action has failed, then the book is not present in the store. Is it?

Upvotes: 0

Views: 331

Answers (1)

curv
curv

Reputation: 3844

Maybe it's the naming used that makes it a red herring, my guess is that ADD_BOOK_FAIL could be in use somewhere else for a different use case as a fall back mechanism.

I agree the way you describe it this doesnt make sense the developer did it for this reason.

Upvotes: 1

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