Choden, Thinley, author

Wolf, E. L

Online Resource

Online Resource

Online Resource

Online Resource

Hayden Library - TP271.K48 2018

Atkins, J. D., 1976- author

Levy, Ian Christopher, author

Horrell, David G., author

McCarraher, Eugene, author

York University Christian Apocrypha Symposium (2015 : Toronto, Ont.),

Twitter Lite uses Redux for state management and relies on code-splitting. However, Redux’s default API is not designed for applications that are incrementally-loaded during a user session.

This post describes how I added support for incrementally loading the Redux modules in Twitter Lite. It’s relatively straight-forward and proven in production over several years.

Redux modules

Redux modules comprise of a reducer, actions, action creators, and selectors. Organizing redux code into self-contained modules makes it possible to create APIs that don’t involve directly referencing the internal state of a reducer – this makes refactoring and testing a lot easier. (More about the concept of redux modules.)

Here’s an example of a small “redux module”.

// data/notifications/index.js

const initialState = [];
let notificationId = 0;

const createActionName = name => `app/notifications/${name}`;

// reducer
export default function reducer(state = initialState, action = {}) {
  switch (action.type) {
    case ADD_NOTIFICATION:
      return [...state, { ...action.payload, id: notificationId += 1 }];
    case REMOVE_NOTIFICATION:
      return state.slice(1);
    default:
      return state;
  }
}

// selectors
export const selectAllNotifications = state => state.notifications;
export const selectNextNotification = state => state.notifications[0];

// actions
export const ADD_NOTIFICATION = createActionName(ADD_NOTIFICATION);
export const REMOVE_NOTIFICATION = createActionName(REMOVE_NOTIFICATION);

// action creators
export const addNotification = payload => ({ payload, type: ADD_NOTIFICATION });
export const removeNotification = () => ({ type: REMOVE_NOTIFICATION });

This module can be used to add and select notifications. Here’s an example of how it can be used to provide props to a React component.

// components/NotificationView/connect.js

import { connect } from 'react-redux';
import { createStructuredSelector } from 'reselect';
import { removeNotification, selectNextNotification } from '../../data/notifications';

const mapStateToProps = createStructuredSelector({
  nextNotification: selectNextNotification
});
const mapDispatchToProps = { removeNotification };

export default connect(mapStateToProps, mapDispatchToProps);

// components/NotificationView/index.js

import connect from './connect';
export class NotificationView extends React.Component { /*...*/ }
export default connect(NotificationView);

This allows you to import specific modules that are responsible for modifying and querying specific parts of the overall state. This can be very useful when relying on code-splitting.

However, problems with this approach are evident once it comes to adding the reducer to a Redux store.

// data/createStore.js

import { combineReducers, createStore } from 'redux';
Import notifications from './notifications';

const initialState = /* from local storage or server */

const reducer = combineReducers({ notifications });
const store = createStore(reducer, initialState);

export default store;

You’ll notice that the notifications namespace is defined at the time the store is created, and not by the Redux module that defines the reducer. If the “notifications” reducer name is changed in createStore, all the selectors in the “notifications” Redux module no longer work. Worse, every Redux module needs to be imported in the createStore file before it can be added to the store’s reducer. This doesn’t scale and isn’t good for large apps that rely on code-splitting to incrementally load modules. A large app could have dozens of Redux modules, many of which are only used by a few components and unnecessary for initial render.

Both of these issues can be avoided by introducing a Redux reducer registry.

Redux reducer registry

The reducer registry enables Redux reducers to be added to the store’s reducer after the store has been created. This allows Redux modules to be loaded on-demand, without requiring all Redux modules to be bundled in the main chunk for the store to correctly initialize.

// data/reducerRegistry.js

export class ReducerRegistry {
  constructor() {
    this._emitChange = null;
    this._reducers = {};
  }

  getReducers() {
    return { ...this._reducers };
  }

  register(name, reducer) {
    this._reducers = { ...this._reducers, [name]: reducer };
    if (this._emitChange) {
      this._emitChange(this.getReducers());
    }
  }

  setChangeListener(listener) {
    this._emitChange = listener;
  }
}

const reducerRegistry = new ReducerRegistry();
export default reducerRegistry;

Each Redux module can now register itself and define its own reducer name.

// data/notifications/index.js

import reducerRegistry from '../reducerRegistry';

const initialState = [];
let notificationId = 0;

const reducerName = 'notifications';

const createActionName = name => `app/${reducerName}/${name}`;

// reducer
export default function reducer(state = initialState, action = {}) {
  switch (action.type) {
    case ADD_NOTIFICATION:
      return [...state, { ...action.payload, id: notificationId += 1 }];
    case REMOVE_NOTIFICATION:
      return state.slice(1);
    default:
      return state;
  }
}

reducerRegistry.register(reducerName, reducer);

// selectors
export const selectAllNotifications = state => state[reducerName];
export const selectNextNotification = state => state[reducerName][0];

// actions
export const ADD_NOTIFICATION = createActionName(ADD_NOTIFICATION);
export const REMOVE_NOTIFICATION = createActionName(REMOVE_NOTIFICATION);

// action creators
export const addNotification = payload => ({ payload, type: ADD_NOTIFICATION });
export const removeNotification = () => ({ type: REMOVE_NOTIFICATION });

Next, we need to replace the store’s combined reducer whenever a new reducer is registered (e.g., after loading an on-demand chunk). This is complicated slightly by the need to preserve initial state that may have been created by reducers that aren’t yet loaded on the client. By default, once an action is dispatched, Redux will throw away state that is not tied to a known reducer. To avoid that, reducer stubs are created to preserve the state.

// data/createStore.js

import { combineReducers, createStore } from 'redux';
import reducerRegistry from './reducerRegistry';

const initialState = /* from local storage or server */

// Preserve initial state for not-yet-loaded reducers
const combine = (reducers) => {
  const reducerNames = Object.keys(reducers);
  Object.keys(initialState).forEach(item => {
    if (reducerNames.indexOf(item) === -1) {
      reducers[item] = (state = null) => state;
    }
  });
  return combineReducers(reducers);
};

const reducer = combine(reducerRegistry.getReducers());
const store = createStore(reducer, initialState);

// Replace the store's reducer whenever a new reducer is registered.
reducerRegistry.setChangeListener(reducers => {
  store.replaceReducer(combine(reducers));
});

export default store;

Managing the Redux store’s reducer with a registry should help you better code-split your application and modularize your state management.

Wegerich, Christine, author

Kerzner, Harold, author

Jahn, Myriam, author

Wartzman, Rick

Interview with Caroline C. Kim, MD, author of Risk of Subsequent Cutaneous Melanoma in Moderately Dysplastic Nevi Excisionally Biopsied but With Positive Histologic Margins

Interview with Megan H. Noe, MD, MPH, MSCE, author of Development and Validation of a Risk Prediction Model for In-Hospital Mortality Among Patients With Stevens-Johnson Syndrome/Toxic Epidermal Necrolysis—ABCD-10

Interview with Jessica Scott, author of Association of Exercise and Swimming Goggles With Modulation of Cerebro-ocular Hemodynamics and Pressures in a Model of Spaceflight-Associated Neuro-ocular Syndrome

The Rise Of Skywalker arrives on Disney Plus on the fourth of May (a date often referred to as Star Wars Day, even though May 25th is and always will be the real Star Wars Day). Time to begin a Star Wars movie marathon. But in which order?

Back when there were a mere two trilogies, this was already a vexing problem if someone were watching the films for the first time. You could watch the six films in episode order:

1. The Phantom Menace
2. Attack Of The Clones
3. Revenge Of The Sith
4. A New Hope
5. The Empire Strikes Back
6. The Return Of The Jedi

But then you’re spoiling the grand reveal in episode five.

Alright then, how about release order?

1. A New Hope
2. The Empire Strikes Back
3. Return Of The Jedi
4. The Phantom Menace
5. Attack Of The Clones
6. Revenge Of The Sith

But then you’re front-loading the big pay-off, and you’re finishing with a big set-up.

This conundrum was solved with the machete order. It suggests omitting The Phantom Menace, not because it’s crap, but because nothing happens in it that isn’t covered in the first five minutes of Attack Of The Clones. The machete order is:

1. A New Hope
2. The Empire Strikes Back
3. Attack Of The Clones
4. Revenge Of The Sith
5. Return Of The Jedi

It’s kind of brilliant. You get to keep the big reveal in The Empire Strikes Back, and then through flashback, you see how this came to be. Best of all, the pay-off in Return Of The Jedi has even more resonance because you’ve just seen Anakin’s downfall in Revenge Of The Sith.

With the release of the new sequel trilogy, an adjusted machete order is a pretty straightforward way to see the whole saga:

1. A New Hope
2. The Empire Strikes Back
3. The Phantom Menace (optional)
4. Attack Of The Clones
5. Revenge Of The Sith
6. Return Of The Jedi
7. The Force Awakens
8. The Last Jedi
9. The Rise Of Skywalker

Done. But …what if you want to include the standalone films too?

If you slot them in in release order, they break up the flow:

1. A New Hope
2. The Empire Strikes Back
3. The Phantom Menace (optional)
4. Attack Of The Clones
5. Revenge Of The Sith
6. Return Of The Jedi
7. The Force Awakens
8. Rogue One
9. The Last Jedi
10. Solo
11. The Rise Of Skywalker

I’m planning to watch all eleven films. This was my initial plan:

1. Rogue One
2. A New Hope
3. The Empire Strikes Back
4. The Phantom Menace
5. Attack Of The Clones
6. Revenge Of The Sith
7. Solo
8. Return Of The Jedi
9. The Force Awakens
10. The Last Jedi
11. The Rise Of Skywalker

I definitely want to have Rogue One lead straight into A New Hope. The problem is where to put Solo. I don’t want to interrupt the Sith/Jedi setup/payoff.

So here’s my current plan, which I have already begun:

1. Solo
2. Rogue One
3. A New Hope
4. The Empire Strikes Back
5. The Phantom Menace
6. Attack Of The Clones
7. Revenge Of The Sith
8. Return Of The Jedi
9. The Force Awakens
10. The Last Jedi
11. The Rise Of Skywalker

This way, the two standalone films work as world-building for the saga and don’t interrupt the flow once the main story is underway.

I think this works pretty well. Neither Solo nor Rogue One require any prior knowledge to be enjoyed.

And just in case you’re thinking that perhaps I’m overthinking it a bit and maybe I’ve got too much time on my hands …the world has too much time on its hands right now! Thanks to The Situation, I can not only take the time to plan and execute the viewing order for a Star Wars movie marathon, I can feel good about it. Stay home, they said. Literally saving lives, they said. Happy to oblige!

Odenbaugh, Jay, author

Wang, Hsiao-Hsuan, author

Dewey Library - KF224.K7 T87 2018

Rotch Library - KF665.Z9 J638 2018

Online Resource

Dewey Library - KF645.A735 2018

Goscha, Christopher E., author