React Components, Props, State and Lifecycles

Elio Struyf
Trainer @ U2U – MVP
October 25th, 2017
Getting up to speed with React

#SPUnite17 - @eliostruyf
A brief moment to the past

DOM Manipulation
HTML JavaScript

Data binding
HTML JavaScript
var app = angular.module('feedbackApp', []);
app.controller('feedbackController', ['$scope', '$http', ($scope,
$http) => {
$scope.oneAtATime = true;
$http.get('tracks.json?ver=0.1').success(data => {
$scope.tracks = data;
});
}]
);
<body data-ng-app="feedbackApp" data-ng-
controller="feedbackController">
<ul id="tracks">
<li data-ng-repeat="track in tracks" class="track">
<h2>{{track.title}}</h2>
<ul class="trackSessions">
<li data-ng-repeat="session in track.sessions"
class="session">
<div class="sessionDetails">
<a data-ng-href="{{session.url}}">{{session.title}}</a>
<span ng-if="session.speaker">by {{session.speaker}}
({{session.start}} - {{session.end}})</span>
<span class="note" ng-
if="session.note">{{session.note}}</span>
</div>
</li>
</ul>
</li>
</ul>
</body>

React is a JavaScript library for
building user interfaces

Components

Component based

React does not separate
component templates

You write HTML in TypeScript

JSX and TSX
Adds XML syntax to JavaScript / TypeScript
<a href="https://www.eliostruyf.com" title="Elio Struyf">My blog</a>
React.createElement("a", { href: "https://www.eliostruyf.com",
title: "Elio Struyf" }, "My blog")
JSX
Plain JavaScript

Variables in JSX / TSX
<a href={blogLink.url} title={blogLink.title}>{blogLink.text}</a>
React.createElement("a", { href: blogLink.url, title:
blogLink.title }, blogLink.text)
Plain JavaScript
JSX

Simple component
class ComponentName extends React.Component<{}, {}> {
public render() {
return (
<div>
Component name should start with a capital letter
</div>
);
}
}

Using the component component
<ComponentName />

Events

Using the component component
class Sample extends React.Component<{}, {}> {
private _linkClick() {
console.log('Hey, you clicked me!');
}
public render(): React.ReactElement<{}> {
return (
<a href="javascript:;" onClick={this._linkClick}>Click me!</a>
);
}
}

How do we convert this?

You don’t have to
worry about it. In
SPFx everything is
already in place.

JSX limitations

Some keywords are reserved in JS / TS
• class à className
• colspan à colSpan
• innerHTML à dangerouslySetInnerHTML
• for à htmlFor
• style à style (it is an object!)

Demo: Component

Inputs (props) and state

Input properties or props
• Passing information to your component
• Do not update properties in your component
• Used for rendering or calculations
<div>
Description: {this.props.description}
</div>

Passing props to components
<ComponentName description="This is the description" />

Component state or state
• Keep hold of the current components variables
• Considered private to the component
constructor(props: IProps) {
super(props);
// initialize the state
this.state = {
show: false
};
}

Update the component state
• Update state by using setState
• Think of it as a request rather than an immediate command
• For better performance, React may delay it
this.setState((prevState, props) => {
return {
show: !prevState.show
};
});

Demo:
Working with
props and states

Listing items

Important things when listing items
• Always use a key
• Try to avoid using then item index
public render() {
const itemList = [{ id: 0, title: "Hello" }, { id: 2, title: "," },
{ id: 4, title: "World" }];
return (
<ul> {
itemList.map(item => {
return <li key={item.id}>{item.title}</li>;
}) }
</ul>
);
}

Virtual DOM

Virtual DOM and change detection
The real DOMVirtual DOM

Demo: Listing items

Lifecycle hooks

Lifecycle hooks
• Mounting:
• constructor, componentWillMount, componentDidMount
• Updating:
• componentWillReceiveProps, shouldComponentUpdate,
componentWillUpdate, componentDidUpdate
• Unmounting
• componentWillUnmount

Calling APIs and storing data

Where to call for data
• Do not do async call in the constructor
• Use the componentDidMount lifecycle hook
public componentDidMount(): void {
this._getAsyncData().then(items => {
if (items) {
this.setState({
items
});
}
});
}

Demo: Retrieving async data

Working with SCSS in SPFx

Demo:
Styling your component

Office Servers & Services MVP
Azure / Office 365 / SharePoint
@eliostruyf
www.eliostruyf.com
info@estruyf.be
Elio Struyf
Lead trainer and architect

React Components, Props, State and Lifecycles

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