var API = {
  get: function() {
    return new Promise(function() {
      // ... some code to get remotely
    });
  }
}

var UserAPI = {
  getById: function(id) {
    return API.get('/users/' + id);
  }
}

var UserActionCreators = {
  requestUserById: function(userId) {
    UserAPI.getById(userId)
      .then(function(data) {
        UserServerActionCreators.handleUserSuccess(data);
      })
      .catch(function() {
        // Notify of error
        UserServerActionCreators.handleUserError(data);
      });
  }
}