angular-cn/public/docs/_examples/lifecycle-hooks/ts/app/spy.directive.ts

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

import { LoggerService } from './logger.service';

let nextId = 1;

// #docregion spy-directive
// Spy on any element to which it is applied.
// Usage: <div mySpy>...</div>
@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 #${nextId++} ${msg}`);
  }
}
// #enddocregion spy-directive