Angular forms / data binding#

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Two-way binding#

• was used in AngularJS 1,x, now replaced with one way bindings via property and event bindung
• can be still used with <input [(ngModel)]="time.hours">
• app.module.ts need to imports: [FormsModule]
• <any [prop]="value" (propChange)="value=$event"></any> is equivalent to <any [(prop)]="value"></any>
• ngOnChange(changes: SimpleChanges) {...} (is also called initially, you can ignore ngOnInit())
• import {SimpleChanges} from '@angular/core';

Event binding #

• (<eventName>)='<method/statement>'
• <button (click)="time.hours=time.hours+1">Plus</button>
• canonical: <button on-click=...
• pseudo events (keydown.enter) (keydown.control.enter) ...
• $event gives access to event data (DOM) like $event.target.value

Interpolation #

• {{property}}
• <div>Time: {{getTime()}}</div>

property binding #

• [<DOM-attrib>]='instance.property'
• <input [value]="time?.hours"/> = safe-navigation operator (time!=null|undefined)
• <input bind-value="time?.hours"/> = canonical binding (equivalent to above)
• [DOM-API|https://developer.mozilla.org/en-US/docs/Web/API/] (html attributes vs dom)
• <td [attr.colspan]="calculateColSpan()"></td> = set atribute directly
• <div [class.alert]="temperatue>100">...</div> = set class directly
• <div [style.font-size.px]="calculateFontSize()">{{temperature}}</div>

Local DOM variables in html #

• #name
• <input #minutes ...> in class available like minutes.focus() (DOM)
• canonical: <input ref-minutes ...>

• @Input = input variable to place into DOM without iteration, iteration through component tag and * @Output

Microsyntax (*)#

• *ngXXX manipulates structure of DOM tree
• ngFor = <template ngFor let-value [ngForOf]="values>
• ngIf = <template [ngIf]="isVisible">

Input / Output#

• @Input()
  • ngOnInit(){...}
  • canonical: @Component({ inputs: ['time',...] )}
• @Output()
  • EventEmitter.emit(value) (Observable, part of RxJS=reactive/async)
  • register for event in other component: (timeChange)="onTimeChanged($event)" ($event=emitted value)
  • canonical: @Component({ outputs: ['time',...] )}

Children#

• @ViewChildren

ngClass#

chapter 6