React+Redux at Scale

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Watch the video with slide
synchronization on InfoQ.com!
https://www.infoq.com/presentations/
react-redux-scale

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www.qconnewyork.com
Purpose of QCon
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knowledge and innovation
Strategy
- practitioner-driven conference designed for YOU: influencers of
change and innovation in your teams
- speakers and topics driving the evolution and innovation
- connecting and catalyzing the influencers and innovators
Highlights
- attended by more than 12,000 delegates since 2007
- held in 9 cities worldwide

Scalability is the capability of a system, network, or process
to handle a growing amount of work, or its potential to be
enlarged to accommodate that growth.
– Wikipedia

Rule: Components should be stateless

Reality: State is the enemy, but also inevitable

onClick(e) {
const value = e.target.value;
const formatted = value.toUpperCase();
this.setState({value: formatted});
}

onClick() {
this.setState((previousState, currentProps) => {
return {
show: !previousState.show,
};
});
}

onClick(e) {
this.setState({value: e.target.value});
this.props.onChange(this.state.value);
}

onClick(e) {
this.setState({value: e.target.value}, () => {
this.props.onChange(this.state.value);
});
}

Rule: Don’t use Context, it hides complexity

Reality: Sometimes complexity should be hidden

class TextCard extends React.Component {
static contextTypes = {
metatypes: React.PropTypes.object,
};
render() {
const {cardData} = this.props;
const {metatypes} = this.context;
return (
<div>
The following is either editable or displayed:
<metatypes.text value={cardData.text} onChange={this.props.onChange} />
</div>
)
}
}
function selectCardComponent(cardData) {
switch (cardData.type) {
case 'text': return TextCard;
default: throw new Error(`Invalid card type ${cardData.type}`);
}
}

const metatypesEdit = {
text: class extends React.Component {
render() {
return <input type="text" {...this.props} />;
}
}
}
const metatypesView = {
text: class extends React.Component {
render() {
return <span>{this.props.value}</span>;
}
}
}

class CardViewer extends React.Component {
static childContextTypes = {
metatypes: React.PropTypes.object
};
getChildContext() {
return {metatypes: metatypesView};
}
render() {
const CardComponent = selectCardComponent(cardData);
return <CardComponent cardData={cardData} />
}
}

class CardEditor extends React.Component {
static childContextTypes = {
metatypes: React.PropTypes.object
};
getChildContext() {
return {metatypes: metatypesEdit};
}
render() {
const CardComponent = selectCardComponent(cardData);
return <CardComponent cardData={cardData} />
}
}

Rule: “Single source of truth” means all state in the store

Reality: You can have multiple “single sources”

this.props.checked = true; this.props.checked = true; this.props.checked = true;
this.state.checked = true;

this.props.checked = true; this.props.checked = true; this.props.checked = true;
this.props.checked = true; checked: true
connect()();

Rule: Side effects should happen outside the Redux cycle

Reality: This doesn’t mean you can’t have callbacks

class ViewPostPage extends React.Component {
componentWillMount() {
const {dispatch, postId} = this.props;
dispatch(fetchPostAction(postId, () => this.logPageLoadComplete()));
}
}

Rule: Redux stores must be normalized for performance

Reality: You must normalize to reduce complexity

https://medium.com/@dcousineau/advanced-redux-entity-normalization-f5f1fe2aefc5

{
byId: {
...entities
},
keyWindows: [`${keyWindowName}`],
[keyWindowName]: {
ids: ['id0', ..., 'idN'],
...meta
}
}

{
byId: {
'a': userA, 'b': userB, 'c': userC, 'd': userD
},
keyWindows: ['browseUsers', 'allManagers'],
browseUsers: {
ids: ['a', 'b', 'c'],
isFetching: false,
page: 1,
totalPages: 10,
next: '/users?page=2',
last: '/users?page=10'
},
allManagers: {
ids: ['d', 'a'],
isFetching: false
}
}

function selectUserById(store, userId) {
return store.users.byId[userId];
}
function selectUsersByKeyWindow(store, keyWindow) {
return store.users[keyWindow].ids.map(userId => selectUserById(store, userId));
}

function reducer(state = defaultState, action) {
switch(action.type) {
case FETCH_USERS:
return {
...state,
keyWindows: uniq([...state.keyWindows, action.keyWindow]),
[action.keyWindow]: {
...state[action.keyWindow],
isFetching: true,
query: action.query
}
};
case RECEIVE_ENTITIES:
return {
...state,
byId: {
...state.byId,
...action.entities.users.byId
},
isFetching: false,
ids: action.entities.users.ids
}
};
}
}

function selectUsersAreFetching(store, keyWindow) {
return !!store.users[keyWindow].isFetching;
}
function selectManagersAreFetching(store) {
return selectUsersAreFetching(store, 'allManagers');
}

case UPDATE_USER:
return {
...state,
draftsById: {
...state.draftsById,
[action.user.id]: action.user
}
};
case RECEIVE_ENTITIES:
return {
...state,
byId: {
...state.byId,
...action.entities.users.byId
},
draftsById: {
...omit(state.draftsById, action.entities.users.byId)
},
isFetching: false,
ids: action.entities.users.ids
}
};
}
}

function selectUserById(store, userId) {
return store.users.draftsById[userId] || store.users.byId[userId];
}

case UNDO_UPDATE_USER:
return {
...state,
draftsById: {
...omit(state.draftsById, action.user.id),
}
};
}
}

Rule: Keep dependencies low to keep the application fast

Reality: Use bundling to increase PERCEIVED performance

class Routes extends React.Component {
render() {
return (
<Switch>
<Route exact path="/"
component={require(‘../home').default} />
<Route path="/admin"
component={lazy(require(‘bundle-loader?lazy&name=admin!../admin’))} />
<Route component={PageNotFound} />
</Switch>
);
}
}

require('bundle-loader?lazy&name=admin!../admin’)

Reality: If you got something render it, update it later

Rule: Scale is bytes served, users concurrent

Reality: Scale is responding to bytes served and users concurrent

Pre: Clear homebrew & yarn caches
1. Reinstall node & yarn via brew
2. Clone repo
3. Run yarn install
4. Run production build
1. Compile & Minify CSS
2. Compile Server via Babel
3. Compile, Minify, & Gzip via Webpack
190.64s
~3 min

Team 1
Team 2
MergeFeatureA
MergeFeatureB
Deploy
Deploy
OMG
ROLLBACK
DEPLOY!!!
MergeFeatureC
MergeBugﬁxforA
Deploy
DeployBLOCKED!!!
Deploy

Team 1
Team 2
MergeFeatureA
MergeFeatureB
Deploy
Deploy
RolloutFlagARolloutFlagBOMG
ROLLBACK
FLAG
A!!!
MergeFeatureC
Deploy
MergeBugﬁxforA
Deploy
RolloutFlagA
RolloutFlagC

Can you optimize your directory structure around team responsibilities?
If teams are organized by “product domain”,
Can you organize code around product domain?

Strict rules rarely 100% apply to your application.
Remembering the purpose behind the rules is valuable.

Code behavior should be predictable and intuitable.
Be realistic about the problem you’re actually solving.

You will not get it perfect the ﬁrst time.
Optimize your processes for refactoring.

Watch the video with slide synchronization on
InfoQ.com!
https://www.infoq.com/presentations/react-
redux-scale

React+Redux at Scale

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