AngularJS ng-init for angular

on-init.directive.spec.ts

import { Component }                 from '@angular/core';
import { ComponentFixture, TestBed } from '@angular/core/testing';
import { OnInitDirective }           from './on-init.directive';

describe('OnInitDirective', () => {
  let component: TestOnInitComponent;
  let fixture: ComponentFixture<TestOnInitComponent>;

  beforeEach(() => {
    TestBed.configureTestingModule({
      declarations: [TestOnInitComponent, OnInitDirective]
    });
    fixture = TestBed.createComponent(TestOnInitComponent);
    component = fixture.componentInstance;
  });

  it('the passed method should be executed on creating the dom element', () => {
    fixture.detectChanges();
    expect(component.isInitialized).toBe(true);
  });
});

@Component({
  template: `<span (onInit)="shouldBeExecuted()"></span>`
})
class TestOnInitComponent {
  public isInitialized = false;

  public shouldBeExecuted(): void {
    this.isInitialized = true;
  }
}

on-init.directive.ts

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

@Directive({
  selector: '[onInit]'
})
export class OnInitDirective implements OnInit {
  @Output()
  public onInit: EventEmitter<void> = new EventEmitter();

  public ngOnInit() {
    this.onInit.emit();
  }
}