React: JSX and Top Level API

Sviluppare applicazioni client, server e mobile con React
Jiayi Hu, Maksim Sinik, Michele Stieven, Fabio Biondi

FABIO BIONDI
FREELANCE
fabiobiondi.io

EX FLASH-FLEX-AIR 
CERTIFIED INSTRUCTOR :°(
2002-2012

I also love: Typescript, Redux, RxJS, D3.js, CreateJS,Arduino, ….
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// 09:50-10:30 
(JsxTopLevelAPI) => <FabioBiondi /> 
 
// 10:30-11:10 
(ReactNative) => <MicheleStieven /> 
 
// 11:10-11:40 
(coffee) => ‘networking’
// 11:40-12:20 
(NextJS) => <MaksimSinik /> 
 
// 12:20-13:00 
(customRenderer) => <JiayiHu />

<JSX>
Top-Level API
vs
Fabio Biondi

JSX
• Many Angular / Javascript developers  
think JSX is sh*t
• Why? Because of the HTML, CSS and JS “mix” 
(in the same ﬁle)

JSX
In my opinion  
JSX is one of the most interesting features in React  
thanks to its ﬂexibility

JSX
• JSX is a preprocessor step that adds XML syntax to JavaScript
• So, you can mix HTML, JS and CSS
• A simple way to update dynamically DOM
• You can deﬁnitely use React without JSX (thanks to React API)  
(but JSX makes React a lot more elegant)

<Widget> should contain several contents:  
React Components or HTML element

PART 1
JSXVS REACT TOP-LEVEL API

COMPONENTS: JSX
import React from ‘react’; 
export const Text = () => {
return <div style={{color: 'red'}}>Hello</div>;
};
<Text />
HOWTO USE:
COMPONENT:
<div>Hello</div>
OUTPUT:

COMPONENT:
COMPONENTS: REACT API
export const Text = () => {
return React.createElement(
'div',
{
style: { color: 'green' }
},
'Hello');
};
<Text />
HOWTO USE:
<div>Hello</div>
OUTPUT:

DYNAMIC CONTENT: JSX
export const Text = props => {
return <div>{props.children}</div>
};
export const Home = () => {
return <Text>Hello World</Text>
};
HOWTO USE:
COMPONENT:

DYNAMIC CONTENT: API
export const Home = () => {
return <Text>Hello World</Text>
};
HOWTO USE:
COMPONENT:
export const Text = props => {
return React.createElement('div', null, props.children);
};

REAL WORLD EXAMPLE
<Text>React</Text>
<Text inline>Hello</Text>
<Text inline>World</Text>
COMPONENT:export const Text = props => {
const type = props.inline ? 'span' : 'div';
return React.createElement(
type, null, props.children
);
};

<Dashboard> <Widget>
COMPONENT:
export const Dashboard = () => {
return (
<div>
<Widget title=“Temperatures” />
<Widget title=“Profile” />
<Widget title=“Anything" />
</div>
)
};
1/2

COMPONENT:
export const Dashboard = () => {
const destroyWidget = () => console.log(‘destroy widget');
const toggleOptions = () => console.log(‘toggle options’);
 
return (
<div>
<Widget
title="Temperatures"
onClose={() => destroyWidget()}
onToggleOptions={() => toggleOptions()} />
</div>
)
<Dashboard> <Widget> 2/2

CREATE A CARD / WIDGET
IN BOOTSTRAP 4
COMPONENT:
<div class="card">
<div class="card-header">Widget Title</div>
<div class="card-body">
Widget Content
</div>
</div>

<Widget />
COMPONENT:
export const Widget = props => {
return (
<div className="card">
<div className="card-header">
<span>{props.title}</span>
<i className="fa fa-gear"
onClick={props.onToggleOptions}></i>
<i className="fa fa-times"
onClick={props.onClose}></i>
</div>
<div className="card-body">
...Widget Content...
</div>
</div>
)
}

<Widget> <WidgetBar>
COMPONENT:
return (
<WidgetBar
title={props.title}
onToggleOptions={props.onToggleOptions}
onClose={props.onClose}
/>
<div className="card-body">
Widget Body
</div>
</div>
)
};

COMPONENT:
const WidgetBar = props => {
return (
<div className="card-header">
<span>{props.title}</span>
<i className="fa fa-gear pull-right"
onClick={props.onToggleOptions} />
<i className="fa fa-times pull-right"
onClick={props.onClose} />
</div>
)
}
<WidgetBar>

type AS CLASS NAME
<Widget title="Temperatures"
type={Chart}
config={temperatures} />
 
<Widget title=“User Profile"
type={Profile}
userID="123"/>
NOTE: each widget needs different properties to work

WidgetBody Content
const Chart = props => (
<h1 className=“m-2">
I'm a chart {props.config.data.length}
</h1>
);
const Profile = props => (
<div className="m-2">
<input type="text" defaultValue={props.userID}/>
...
</div>
);
const Any = props => `I’m another component`;

COMPONENT:
return (
<WidgetBar
title={props.title}
onToggleOptions={props.onToggleOptions}
onClose={props.onClose}
/>
<WidgetBody {...props} />
</div>
)
}; NOTE: we use spread operator … to pass all props to a component
<Widget> <WidgetBody>

<WidgetBody>
const WidgetBody = props => {
const {
type, title, onToggleOptions, onClose, ...others
} = props;
 
return React.createElement(type, {...others}, null);
}
NOTE: we use ES6 destructuring

PART 5
type AS STRING
(USEFUL WHEN WIDGET CONFIGURATION 
IS LOADED FROM JSON)

HOWTO USE
COMPONENT:
<Widget title=“Temperatures"
type="Chart"
config={myData}  
onShowOptions={() => openOptions()} />
<Widget title="MyProfile"
type="Profile"
user=“123" 
onShowOptions={() => openOptions()} />
<Widget title=“Any Component"
type="Any"/>

or by using .map()
COMPONENT:
props.widgets.map(item => (
<Widget
key={item.id}
{...item}
onShowOptions={() => openOptions()}
/> 
);

<widgetBody>: JSX version
COMPONENT:
switch(props.type) {
case 'Chart': return <Chart {...props} />;
case 'Profile': return <Profile {...props} />;
case 'Any': return <Any {...props} />;
default: return <h3>You forgot type</h3>;
}
};

<WidgetBody>: REACT API/eval version
COMPONENT:
const { type, ...others } = props;
 
return React.createElement( eval(type), {...others}, null )
}
If you run eval() someone could run malicious code on the user's machine

<widgetBody>: API & Map() version
COMPONENT:
const { type, ...others } = props;
return React.createElement( 
components.get(type), {...others}, null
)
}
const components = new Map();
components.set('Chart', Chart);
components.set('Profile', Profile);
components.set('Any', Any);

CAN I DOTHE SAME  
IN ANGULAR?

CREATING A DIRECTIVE: 
<div
[widgetBody]=“myComponent”
(close)=“destroy()”
(toggleOptions)=“toggleMenu()”>

import {
ComponentRef, ComponentFactoryResolver, Directive, ElementRef, Input, OnDestroy, ViewContainerRef
} from '@angular/core'; 
@Directive({
selector: '[widgetBody]'
})
export class WidgetBodyDirective implements OnDestroy {
@Input() set widgetBody(component: WidgetComponent) {
this.view.clear();
if (component) {
let factory = this.resolver.resolveComponentFactory(component.type);
this.ref = this.view.createComponent(factory);
for (let key in component.payload) {
this.ref.instance[key] = component.payload[key];
}
}
} 
private ref: ComponentRef<any>;
constructor( private view: ViewContainerRef, private resolver: ComponentFactoryResolver) { }
ngOnDestroy() {
if (this.ref) {
this.ref.destroy();
}
}
}

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