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Angular 2 - The Next Framework
Angular 2 – The Next Framework
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
Angular 2 features
• Optimized for both desktop and mobile
• Ahead of Time (AoT) compilation
• Incredible performances
• Native Reactive support
@Injectable
@Injectable
export class MyService { getData() { return this.loadData.load(); } }
@Injectable
import { Injectable } from 'angular2/core';
@Injectable() export class MyService { constructor(private loadData:LoadData) {} getData() { return this.loadData.load(); } }
@Component
@Component
import { Component } from '@angular/core'; @Component({ selector: 'commit-hello', template: '<p>Hello, {{name}}</p>' }) export class Hello { name: string; constructor() { this.name = 'World'; } }
@Directive
@Directive
import { Directive, HostListener } from '@angular/core'; @Directive({ selector: '[confirm]' }) export class ConfirmDirective { @HostListener('click', ['$event']) confirmFirst(event: Event) { return window.confirm( 'Are you sure you want to do this?'); } }
@Directive
// Usage <button type="button" (click)="visitOtherPage()" confirm>Visit another page</button>
@Directive – ngFor example
<ul> <li *ngFor="let doctor of doctors; let idx = index"> Doctor #{{idx}} - {{doctor.name}} </li> </ul>
@Pipe
@Pipe
import { Component } from '@angular/core'; @Component({ selector: 'product-price', template: '<p>Price: {{ price | currency }}</p>' }) export class ProductPrice { price: number = 99.99; }
@Pipe
import { Pipe, PipeTransform } from '@angular/core'; const UNITS = ['B', 'KB', 'MB', 'GB']; @Pipe({ name: 'formatFileSize' }) export class FormatSize implements PipeTransform { transform(bytes: number=0, precision: number=2) : string { if (!isFinite(bytes)) return '?'; let unit = 0; while ( bytes >= 1024 ) { bytes /= 1024; unit ++; } return bytes.toFixed(precision) + ' ' + UNITS[unit]; } }
HTTP services
HTTP services
import {Injectable} from '@angular/core'; import {Http, Response} from '@angular/http'; import {Observable} from 'rxjs'; import {Hero} from './hero'; @Injectable() export class LoadDataService { constructor(private http: Http) {} search(term: string): Observable<Hero[]> { return this.http .get(`app/heroes/?name=${term}`) .map((r: Response) => r.json().data as Hero[] ); } }
TypeScript
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
• 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
@Component – selector
import { Component } from '@angular/core'; @Component({ selector: 'commit-hello', template: '<p>Hello, {{name}}</p>' }) export class Hello { name: string; constructor() { this.name = 'World'; } }
@Component – selector
selector is the element property that we use to tell Angular to create and insert an instance of this component.
@Component – template
• 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, e.g. {{1+1}}
• property binding [attribute]="propertyName" – 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.
@Component – inputs
import { Component, Input } from '@angular/core'; @Component({ selector: 'commit-hello', template: '<p>Hello, {{name}}</p>' }) export class Hello { @Input() name: string; }
@Component – inputs
import { Component } from '@angular/core'; @Component({ selector: 'commit-hello', inputs: ['name'] template: '<p>Hello, {{name}}</p>' }) export class Hello { }
@Component – inputs
// To bind to a raw string <commit-hello name="World"></commit-hello>
// To bind to a variable in the parent component <commit-hello [name]="userName"></commit-hello>
@Component – outputs
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.count++; this.result.emit(this.count); } }
@Component – child components
import { Component, ViewChild } from '@angular/core'; import { Alert } from './alert.component'; @Component({ selector: `app`, template: `<alert>My alert</alert> <button (click)="showAlert()">Show Alert</button>` }) export class App { @ViewChild(Alert) alert: Alert; showAlert() { this.alert.show(); } }
@Component – child componentsimport { Component, ViewChild } from '@angular/core'; import { Alert } from './alert.component'; @Component({ selector: `app`, template: `<alert>My alert</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); } }
@Component – transclusion
import { Component, Input } from '@angular/core'; @Component({ selector: `commit-hello`, template: `<div><p>Hello, {{name}}</p> <ng-content><p>No extra data</p></ng-content> </div>`}) export class Hello { @Input() name: string; } //Usage <commit-hello name="Andrea"> <div> <h1>Some other data</h1> <p>Some text</p> </div> </commit-hello>
Component lifecycle
Components & Directives shared lifecycle
Method Decription
ngOnChanges input property value changes
ngOnInit initialization step
ngDoCheck every change detection cycle
ngOnDestroy before destruction
@Component – lifecycle
import { Component, OnInit } from '@angular/core'; @Component({ selector: 'commit-hello', template: '<p>Hello, {{name}}</p>' }) export class Hello implements OnInit { name: string; constructor() { this.name = 'World'; } ngOnInit() { // do something to initialize the component } }
@Directive – lifecycle
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>
Lifecycle
“Angular only calls a directive/component hook method if it is defined.”
– Angular official docs
Component styles
Inline styles
import { Component } from '@angular/core';
const baseStyle = { backgroundColor: 'green', padding: '10px' };
@Component({ selector: 'commit-hello', template: '<p [ngStyle]="style">Hello!</p>' }) export class Hello { style: any = baseStyle; }
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.
View encapsulation – example (1/2)
import { Component, ViewEncapsulation } from '@angular/core';
@Component({ selector: 'commit-hello', styles:[` .main { background-color: green; padding: 10px; } `], encapsulation: ViewEncapsulation.Emulated, template: '<p class="main">Hello!</p>' }) export class Hello { }
View encapsulation – example (2/2)
//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!
Observables
“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…”
– Angular official docs
Stream
“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.”
– A. Staltz
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.
Observable (1/2)
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) => console.log(`Value ${value}`), (error) => console.log(`Error!!!`), () => console.log(`Completed`) );
Observable (2/2)
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 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.
Define a module// app.modules.ts import { BrowserModule } from '@angular/platformbrowser'; 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 {}
Bootstrapping Angular
// main.ts import { platformBrowserDynamic } from '@angular/platform-browser-dynamic'; import { AppModule } from './app/';
// Bootstrap main component platformBrowserDynamic().bootstrapModule(AppModule);
angular-cli
• Angular command line interface• Works with Node.js and npm• Fast project setup:
• npm install -g angular-cli • ng new <project name> • cd <project name> • ng serve
Under the hood
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
Change Detection
“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.”
– ngBook2
Change Detection
@Component({ template: '<v-card [vData]="vData"></v-card>' }) class VCardApp { constructor() { this.vData = { name: 'Andrea Vallotti', email: '[email protected]' } } changeData() { this.vData.name = 'Pascal Precht'; } }
Change Detection
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Change Detection
• Every component gets a change detector responsible for checking the bindings defined in its template
• Change detection strategies:• default: update the component every time data changes• on push: update the component only when its inputs change or the
component requests to be updated
Immutable objects
var vData1 = someAPIForImmutables.create({ name: 'Pascal Precht' });
var vData2 = vData1.set('name', 'Andrea Vallotti');
vData1 === vData2 // false
Change Detection - OnPush
@Component({ template: '<h2>{{vData.name}}</h2> <span>{{vData.email}}</span>', changeDetection: ChangeDetectionStrategy.OnPush }) class VCardCmp { @Input() vData; }
Change Detection – OnPush + Immutables
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Change Detection - OnPush@Component({template: '{{counter}}', changeDetection: ChangeDetectionStrategy.OnPush }) class CartBadgeCmp { @Input() addItemStream:Observable<any>; counter = 0; constructor(private cd: ChangeDetectorRef) {} ngOnInit() { this.addItemStream.subscribe(() => { this.counter++; // application state changed this.cd.markForCheck(); // marks path }); } }
Change Detection – OnPush + Observables
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Links & credits
• Matteo Ronchi – @cef62, https://github.com/cef62
• https://github.com/commit-university/exploring-angular-2
• http://pascalprecht.github.io/slides/angular-2-change-detection-explained/#/
• https://angular.io/docs/ts/latest/
