85 lines
2.0 KiB
TypeScript
85 lines
2.0 KiB
TypeScript
// #docregion
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import {
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Component, Input,
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OnChanges, SimpleChanges,
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} from '@angular/core';
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import { LoggerService } from './logger.service';
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@Component({
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selector: 'my-counter',
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template: `
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<div class="counter">
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Counter = {{counter}}
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<h5>-- Counter Change Log --</h5>
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<div *ngFor="let chg of changeLog" mySpy>{{chg}}</div>
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</div>
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`,
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styles: ['.counter {background: LightYellow; padding: 8px; margin-top: 8px}']
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})
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export class MyCounterComponent implements OnChanges {
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@Input() counter: number;
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changeLog: string[] = [];
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ngOnChanges(changes: SimpleChanges) {
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// Empty the changeLog whenever counter goes to zero
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// hint: this is a way to respond programmatically to external value changes.
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if (this.counter === 0) {
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this.changeLog.length = 0;
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}
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// A change to `counter` is the only change we care about
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let chng = changes['counter'];
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let cur = chng.currentValue;
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let prev = JSON.stringify(chng.previousValue); // first time is {}; after is integer
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this.changeLog.push(`counter: currentValue = ${cur}, previousValue = ${prev}`);
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}
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}
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/***************************************/
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@Component({
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selector: 'counter-parent',
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template: `
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<div class="parent">
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<h2>Counter Spy</h2>
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<button (click)="updateCounter()">Update counter</button>
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<button (click)="reset()">Reset Counter</button>
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<my-counter [counter]="value"></my-counter>
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<h4>-- Spy Lifecycle Hook Log --</h4>
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<div *ngFor="let msg of spyLog">{{msg}}</div>
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</div>
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`,
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styles: ['.parent {background: gold;}'],
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providers: [LoggerService]
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})
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export class CounterParentComponent {
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value: number;
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spyLog: string[] = [];
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private logger: LoggerService;
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constructor(logger: LoggerService) {
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this.logger = logger;
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this.spyLog = logger.logs;
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this.reset();
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}
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updateCounter() {
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this.value += 1;
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this.logger.tick();
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}
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reset() {
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this.logger.log('-- reset --');
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this.value = 0;
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this.logger.tick();
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}
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}
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