newsletterFormReducer.js

const newsletterFormReducer = (state, action) => {
  const { type, payload } = action;

  switch (type) {
    case actionTypes.SET_NEWSLETTERS_OPTIONS:
      return {
        ...state,
        isLoading: payload.newsletterOptions.length === 0,
        fields: {
          ...state.fields,
          newsletter: {
            ...state.fields.newsletter,
            options: payload.newsletterOptions,
          },
        },
      };

    case actionTypes.CHANGE_FIELD:
      return withValidation(state, payload.field, payload.value);

    default:
      return state;
  }
};