Exploring Angular 2

Angular 2

The Next Framework

@cef62

github.com/cef62

Senior frontend engineer @

Staff member of Frontenders Verona

Italian React & Angular Communities Maintainer

MATTEO RONCHI

AngularJS history

• AngularJS was originally developed in 2009 by Misko Hevery and Adam Abrons

• Misko Hevery started to work for Google in 2009

• 1st release of AngularJS: 1 developer, 3 weeks, 1000 loc

• AngularJS version 1.0 was released in 2012 by Google

• Angular version 2 was released in September 2016 after 2 years development

WELCOME TO THE FUTURE

Angular 2 features

• Optimized for both desktop and mobile

• Ahead of Time (AoT) compilation

• Incredible performances

• Native Reactive support

ANGULAR 2 BASICS

@INJECTABLE

export class MyService {

getData() { return this.loadData.load(); } }

import { Injectable } from `angular2/core`;

@Injectable() export class MyService { constructor(private loadData:LoadData) {}

getData() { return this.loadData.load(); } }

ANGULAR 2 BASICS

@COMPONENT

import { Component } from '@angular/core';

@Component({ selector: 'hello', template: '<p>Hello, {{name}}</p>' }) export class Hello { name: string;

constructor() { this.name = 'World'; } }

ANGULAR 2 BASICS

@DIRECTIVE

import { Directive, HostListener } from '@angular/core';

@Directive({ selector: `[confirm]` }) export class ConfirmDirective {

@HostListener(`click`, [`$event`]) confirmFirst(event: Event) { return window.confirm( `Are you sure you want to do this?` ); } }

// Usage <button type="button" (click)="visitOtherPage()" confirm>Visit another page</button>

ANGULAR 2 BASICS

@PIPES

import { Component } from '@angular/core';

@Component({ selector: `product-price`, template: `<p>Price: {{ price | currency }}</p>` }) export class ProductPrice { price: number = 99.99; }

import { Pipe, PipeTransform } from '@angular/core';

const UNITS = ['B', 'KB', 'MB', 'GB'];

@Pipe({ name: 'formatFileSize' }) export class FormatSize implements PipeTransform { transform( bytes: number = 0, precision: number = 2 ) : string {

if (!isFinite(bytes)) return ‘?';

let unit = 0; while ( bytes >= 1024 ) { bytes /= 1024; unit ++; }

return bytes.toFixed(precision) + ' ' + UNITS[unit]; } }

ANGULAR 2 BASICS

HTTP SERVICE

import {Injectable} from '@angular/core'; import {Http, Response} from '@angular/http'; import {Observable} from 'rxjs'; import {Hero} from './hero';

@Injectable() export class LoadDataService { constructor(private http: Http) {}

search(term: string): Observable<Hero[]> { return this.http .get(`app/heroes/?name=${term}`) .map((r: Response) => { return r.json().data as Hero[] }); } }

IN THE ZONE

AngularJS $digest cycle

• AngularJS engine is built using a dirty checking algorithm.

• Application state is a single entity connected to every visual component and calculated every time a component mutates some data

• It’s very easy to trigger unwanted $digest cycles impacting performances

• Very difficult to debug

Angular 2 Change Detection engine

• Based on ngZone

• Recalculate the components tree state after every async interaction (events, timers, observables..)

• Every component has its own Change Detector

• Component’s Change Detector is generated at runtime to improve performances

• Developers can control how and when components are recalculated

– ngBook2

“When one of the components change, no matter where in the tree it is, a change

detection pass is triggered for the whole tree, from top to bottom.”

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CHANGE DETECTION TRAVELS TOP TO BOTTOM

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CHANGE DETECTION IS DEFINED AT COMPONENT LEVEL

• Every component gets a change detector responsible for checking the bindings defined in its template

• ChangeDetectionStrategy

• default: update the component every time data changes

• onPush: update the component only when its inputs change or the component requests to be updated

CHANGE DETECTION (onPush) WITH IMMUTABLE DATA

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CHANGE DETECTION (onPush) WITH OBSERVABLES

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TYPESCRIPT: A FIRST CLASS CITIZEN

Why typescript

• Angular2 Dependency Injection system is based on type reflection

• Annotations offer a powerful and very expressive way to describe elements

Pros

• Improve Developer Experience with better tools

• Compile time error check

• Type safety

• Better documentation

• Easy to adopt for backend developers

Cons

• Increase project’s technical debt

• Slower learning curve for traditional javascript developer

• Impossible to remove without a complete rewrite

THINKING COMPONENTS

Modern web is all about components

• Thinking of components instead of views improves decoupling and separation of concerns

• Components are composable and highly reusable

• Easier to test

• UX and UI teams integrate better

A component is

• exported as a custom HTML tag: <tab-bar />

• defined by an HTML template

• enhanced using the @component decorator

• controlled using its inputs and outputs

• initialized by Angular Dependency Injection engine

SELECTOR

@COMPONENT

import { Component } from '@angular/core';

@Component({ selector: 'hello', template: '<p>Hello, {{name}}</p>' }) export class Hello { name: string;

constructor() { this.name = 'World'; } }

selector is the element property that we use to tell Angular to create and insert an instance of this component.

COMPONENT TEMPLATE

@COMPONENT

template is an HTML string that tells Angular what needs to be to rendered in the DOM.

templateUrl is a relative path to a file containing the component HTML string.

TEMPLATE SYNTAX

• template tags {{ expression }}: Execute arbitrary expressions. Eg: {{1+1}.

• property binding [key]=“value”. Used to pass data to a component.

• event binding (event)=“expression”. Expression executed anytime the registered event fires.

• 2-way binding <input [(ngModel)]=“u.name"> Requires to import `FormsModule` to be used.

INPUTS

@COMPONENT

import {Component, Input} from `@angular/core`;

@Component({ selector: `hello`, template: `<p>Hello, {{name}}</p>` }) export class Hello { @Input() name: string; }

import { Component } from `@angular/core`;

@Component({ selector: `hello`, inputs: [`name`], template: `<p>Hello, {{name}}</p>` }) export class Hello {}

// To bind to a raw string <hello name="World"></hello>

// To bind to a variable in the parent scope <hello [name]="userName"></hello>

OUTPUTS

@COMPONENT

import {Component} from `@angular/core`;

@Component({ selector: `counter`, template: ` <div> <p>Count: {{ num }}</p> <button (click)="increment()">Increment</button> </div> ` }) export class Counter { num: number = 0;

increment() { this.num++; } }

import { Component, EventEmitter, Output } from `@angular/core`;

@Component({ selector: `counter`, template: ` <div> <p>Count: {{ count }}</p> <button (click)="increment()">Increment</button> </div> ` }) export class Counter { count: number = 0; @Output() result: EventEmitter = new EventEmitter();

increment() { this.result.emit(this.count); } }

CHILD COMPONENTS

@COMPONENT

import {Component, ViewChild} from `@angular/core`; import {Alert} from `./alert.component`;

@Component({ selector: `app`, template: ` <my-alert>My alert</my-alert> <button (click)="showAlert()">Show Alert</button>` }) export class App { @ViewChild(Alert) alert: Alert;

showAlert() { this.alert.show(); } }

import {Component, ViewChild} from `@angular/core`; import {Alert} from `./alert.component`;

@Component({ selector: `app`, template: ` <my-alert>My alert</my-alert> <input #msg type=“text” /> <button (click)="showAlert()">Show Alert</button>` }) export class App { @ViewChild(Alert) alert: Alert; @ViewChild(`msg`) msgInput;

showAlert() { const txt = this.msgInput.nativeElement.value; this.alert.show(txt); } }

CONTENT TRANSCLUSION

@COMPONENT

import {Component, Input} from `@angular/core`;

@Component({ selector: `hello`, template: `<div> <p>Hello, {{name}}</p> <ng-content><p>No extra data</p></ng-content> </div>` }) export class Hello { @Input() name: string; }

// Usage

<hello name=“Matteo”> <div> <h1>Some other data</h1> <p>Some text</p> </div> </hello>

COMPONENT LIFECYCLE

Components & Directives shared lifecycle

ngOnChanges input property value changes

ngOnInit Initialization step

ngDoCheck every change detection cycle

ngOnDestroy before destruction

import { Component, OnInit } from '@angular/core';

@Component({ selector: 'hello', template: '<p>Hello, {{name}}</p>' }) export class Hello implements OnInit { name: string;

constructor() { this.name = 'World'; }

ngOnInit() { // do something to initialize the component } }

import { Directive, OnInit, OnDestroy } from '@angular/core';

@Directive({ selector: `[mySpy]` }) export class SpyDirective implements OnInit, OnDestroy {

constructor(private logger: LoggerService) { }

ngOnInit() { this.logIt(`onInit`); }

ngOnDestroy() { this.logIt(`onDestroy`); }

private logIt(msg: string) { this.logger.log(`Spy ${msg}`); } }

// Usage <div mySpy>...</div>

–Angular official docs

“Angular only calls a directive/component hook method if it is defined.”

COMPONENT STYLE

INLINE STYLES

import { Component } from '@angular/core';

const baseStyle = { backgroundColor: 'green', padding: '10px' }; @Component({ selector: 'hello', template: ‘<p [ngStyle]="style">Hello!</p>' }) export class Hello { style: any = baseStyle; }

COMPONENT STYLE

VIEW ENCAPSULATION

• Emulated (default) - styles from main HTML propagate to the component. Styles defined in this component's @Component decorator are scoped to this component only.

• Native (shadow DOM)- styles from main HTML do not propagate to the component. Styles defined in this component's @Component decorator are scoped to this component only.

• None - styles from the component propagate back to the main HTML and therefore are visible to all components on the page.

———

Be careful with apps that have None and Native components mixed in the application. All components with None encapsulation will

have their styles duplicated in all components with Native encapsulation.

import { Component, ViewEncapsulation } from '@angular/core';

@Component({ selector: ‘hello', styles: [` .main { background-color: green; padding: 10px; } `], encapsulation: ViewEncapsulation.Emulated, template: `<p class="main">Hello!</p>` }) export class Hello {}

// OUTPUT HTML <p class="main" _ngcontent-yok-5="" >Hello!</p>

// output css (inside <head>) .main[_ngcontent-yok-5] { background-color: green; padding: 10px; }

BE REACTIVE!

OBSERVE ALL THE THINGS!

–Angular official docs

“Observables open up a continuous channel of communication in which multiple values of data can be emitted over time […] Angular 2 uses

observables extensively - you'll see them in the HTTP service and the event system…”

–A. Staltz

“A stream is a sequence of ongoing events ordered in time. It can emit 3 different things: a

value, an error, or a "completed" signal. Consider that the "completed" takes place, for instance, when the current window is closed.”

OBSERVABLES vs PROMISES

• Both provide us with abstractions that help us deal with the asynchronous nature of our applications.

• Observables are cancellable.

• Observables can be retried using one of the retry operators provided by the API, such as retry and retryWhen.

• Promises require the caller to have access to the original function that returned the promise in order to have a retry capability.

import { Observable } from ‘rxjs/Observable';

const dataStream = new Observable((observer) => { setTimeout(() => { observer.next(42); }, 1000);

setTimeout(() => { observer.next(43); }, 2000);

setTimeout(() => { observer.complete(); }, 3000); });

const subscription = dataStream.subscribe( (value) => this.values.push(value), (error) => this.anyErrors = true, () => this.finished = true );

import { Component, OnInit, ViewChild } from `@angular/core`; import { Observable } from 'rxjs';

@Component({ selector: `app`, template: `<input type="text" #username />` }) export class App implements OnInit { @ViewChild(`username`) username: any;

ngOnInit(): void { Observable .fromEvent(this.username.nativeElement, 'keyup') .map((e: any) => e.target.value) .filter((text: string) => text.length > 5) .debounceTime(1000) .subscribe((text: string) => this.submit(text)); }

submit(text: string): void { console.log('submitted: ', text); } }

Bootstrapping Angular

Bootstrapping is an essential process in Angular - it is where the application is loaded when Angular comes to life.

Bootstrapping Angular 2 applications is certainly different from Angular 1.x, but is still a straightforward procedure.

// app.modules.ts

import { BrowserModule } from '@angular/platform-browser'; import { NgModule } from '@angular/core'; import { HttpModule } from '@angular/http'; import { AppComponent } from './[PATH]/app.component'; import { MyComponent } from ‘./[PATH]/some.component'; import { SomeService } from “./[PATH]/some.service";

@NgModule({ declarations: [AppComponent, MyComponent], providers: [SomeService], imports: [BrowserModule, HttpModule], bootstrap: [AppComponent] }) class AppModule {}

// main.ts

import { platformBrowserDynamic } from '@angular/platform-browser-dynamic'; import { AppModule } from './app/';

// Bootstrap main component platformBrowserDynamic().bootstrapModule(AppModule);

angular-cli

FAST PROJECT SETUP

WORKING EXAMPLE: github.com/commit-university/exploring-angular-2

THANKS!

@CEF62