Advanced React Component Patterns - ReactNext 2018

BEYOND CONTAINERS &
PRESENTATIONAL COMPONENTS
Advanced
Patterns

Data Down Actions Up
Unidirectional Data Flow
vs
Model Binding

Presentational
and Container
Components

“React bindings for Redux separate
presentational components from
container components. This
approach can make your app easier to
understand and allow you to more
easily reuse components.”
— Redux Documentation

Presentational
Components
Container Components
Purpose
How things look (markup,
styles)
How things work (data fetching, state
updates)
Aware of
Redux
No Yes
To read data Read data from props Subscribe to Redux state
To change
data
Invoke callbacks from props Dispatch Redux actions
Are written By hand Usually generated by React Redux

const MyGreeting = ({ name }) !=>
<h1>Hello {name}!</h1>;
const mapStateToProps = state !=> ({
name: state.name
});
export default connect(mapStateToProps)
(MyGreeting);

Container
Know things about outside (context)
Presentational
Have everything passed in (pure)

Class Component
Function Component

Hold on…
Class Components also store state.
That’s not “outside”?

Is state really inside the component?
How does the React lifecycle work?

class MyComponent extends
React.Component

Where is the class component
in Redux containers?

connect()
Higher Order Component

const hoc = WrappedComponent !=>
class HOC extends React.Component {
render() {
return <WrappedComponent !/>;
}
};

container
presentation
pure class
functionhigher order
component
noise

Pure Component
Side Effect Component

How did that component do that….

Victory Charts
const data = […];
return (
<VictoryChart height={390}>
<VictoryLine data={data} !/>
<VictoryScatter
data={data}
size={5}
!/>
!</VictoryChart>
);

const data = […];
return (
<VictoryChart height={390}>
<VictoryLine data={data} !/>
<VictoryScatter
data={data}
size={5}
!/>
!</VictoryChart>
);
Victory Charts

This looks like
bi-directional communication

<VictoryChart !/>
interrogates its children

Pure Side Effect
Component
Child Aware

Best Code Comment Award
Nominee

Wizard
<Wizard>
<Step>This is step one. Click next to continue!</Step>
<Step>This is the last step. Well done.!</Step>
!</Wizard>

export default class Wizard extends React.Component {
state = {
furthestStep: 0
};
completeStep = furthestStep !=> {
this.setState({ furthestStep });
};
render() {
const { children } = this.props;
return (
<React.Fragment>
{React.Children.toArray(children).reduce(
(acc, child, index) !=>
index > this.state.furthestStep
? acc
: [
!!...acc,
React.cloneElement(child, {
onComplete: () !=> this.completeStep(index + 1)
})
]
, [])}
!</React.Fragment>
);
}
}

state = {
furthestStep: 0
};
completeStep = furthestStep !=> {
this.setState({ furthestStep });
};

{React.Children.toArray(children).reduce(
(acc, child, index) !=>
index > this.state.furthestStep
? acc
: [
!!...acc,
React.cloneElement(child, {
onComplete: () !=> this.completeStep(index + 1)
})
],
[]
)}

Pure Side Effect
Component
Child Aware
Child Enhancing

Framework Code,
Not Application Code!

but not presentational
All Pure Components

Data In, HTML (UI) Out
How things look (markup, styles)
Presentational Components

Pure Side Effect
Component
Child Aware
Child Enhancing
Presentation

import Desktop from './MyComponent.desktop';
import Mobile from './MyComponent.mobile';
let MyComponent = Responsive({ Mobile, Desktop });
export default MyComponent;

export const MOBILE_QUERY = '(max-width: 767px)';
export const isMobile = () !=>
(window.matchMedia ? window.matchMedia(MOBILE_QUERY).matches : false);
!/* This assumes only two breakpoints. It can become more sophisticated !*/
export default ({ Mobile, Desktop }) !=>
class Responsive extends Component {
render() {
return (
<MediaQuery query={MOBILE_QUERY}>
{matches !=> (
matches ?
<Mobile {!!...this.props} !/> :
<Desktop {!!...this.props} !/>)}
!</MediaQuery>
);
}
};

Trade off:
Simplicity vs Dryness

Pure Side Effect
Component
Child Aware
Child Enhancing
Presentation Decision

const MyContext = React.createContext(defaultValue);
<MyContext.Provider value={!/* some value !*/}>
…
!</MyContext.Provider>
class MyComponent extends React.Component {
static contextType = MyContext;
}
<MyContext.Consumer>
{value !=> !/* render something based on the context value !*/}
!</MyContext.Consumer>

const Analytics = React.createContext();
const tracker = new AnalyticsService(config);
const el = document.querySelector(‘#mount-target');
ReactDOM.render(
<Analytics.Provider tracker={tracker}>
<App !/>
!</Analytics.Provider>,
el
);

class ExampleDownloadButton extends React.Component {
onClick = () !=> {
const { tracker } = this.props;
tracker.track('download.button.clicked');
};
render() {
return (
<Button onClick={this.onClick}>
<Icon name="cloud-download" size={16} !/>
Download
!</Button>
);
}
}
export default withTracker(ExampleDownloadButton);

Pure Side Effect
Component
Child Aware
Child Enhancing
Presentation Decision Service

Feature Toggle Component or
Authentication Component
Decision + Service Component

const NewComponent = () !=> (
<p>This is only for beta users!</p>
);
const OldComponent = () !=> (
<p>This is for normal users!</p>
);
export default withFeature('betaFeature')({
new: NewComponent,
old: OldComponent
});

import TheComponent from './the-component';
const Page = () !=> (
<div>
<TheComponent !/>
!</div>
);

const features = new FeatureService(config);
const el = document.querySelector(‘#mount-target');
ReactDOM.render(
<FeatureProvider features={features}>
<App !/>
!</FeatureProvider>,
el
);

Observables, high performance etc

Pure Side Effect
Component
Child Aware
Child Enhancing
Presentation Decision Service Event Listener

const Card = styled.div`
max-width: 600px;
`;
<styled.div id=“my-component">
!</styled.div>

Pure Side Effect
Component
Child Aware
Child Enhancing
Presentation Decision Service Event Listener Styled

Why do developers care about patterns?

The Magical Number Seven,
Plus or Minus Two:
Some Limits on Our Capacity for
Processing Information
—one of the most highly cited
papers in psychology

How did that component do that….
reduce the number of times you ask

Why separate pure vs side effects?

Pure components are:
•Easier to reason about
•Easier to test
•Easier to compose
•Generally simpler

Functional Core,
Imperative Shell
— Gary Bernhardt

🔥 
How do Hooks affect this?

import { useState } from 'react';
function Example() {
!// Declare a new state variable, which we'll call "count"
const [count, setCount] = useState(0);
return (
<div>
<p>You clicked {count} times!</p>
<button onClick={() !=> setCount(count + 1)}>
Click me
!</button>
!</div>
);
}

Class Component
Pure Component

class component = side effects
Hooks = side effects

In real code bases the split is
almost never perfectly clear. 
 
Hooks make side effects easier.
No reason to stop separating concerns.

Advanced React Component Patterns - ReactNext 2018

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