Why isn't ngOnInit() called when an Injectable class is resolved?
Code
import {Injectable, OnInit} from 'angular2/core'; import { RestApiService, RestRequest } from './rest-api.service'; @Injectable() export class MovieDbService implements OnInit { constructor(private _movieDbRest: RestApiService){ window.console.log('FROM constructor()'); } ngOnInit() { window.console.log('FROM ngOnInit()'); } } Console Output
FROM constructor() Lifecycle hooks, like OnInit() work with Directives and Components. They do not work with other types, like a service in your case. From docs:
A Component has a lifecycle managed by Angular itself. Angular creates it, renders it, creates and renders its children, checks it when its data-bound properties change and destroy it before removing it from the DOM.
Directive and component instances have a lifecycle as Angular creates, updates, and destroys them.
ngOnInit logic to the constructor for Injectable classes? I just remembered reading that you should keep any logic out of the constructor for whatever reason.
providers arrays. If you want a singleton service, put it in your main module's providers, and if you want per-component services add them to the component directly.
ngOnDestroy is called for injected servicesI don't know about all the lifecycle hooks, but as for destruction, ngOnDestroy actually get called on Injectable when it's provider is destroyed (for example an Injectable supplied by a component).
From the docs :
Lifecycle hook that is called when a directive, pipe or service is destroyed.
Just in case anyone is interested in destruction check this question:
ngOnInit isn't called :-( I really wanted to do some transparent delayed initialization magic. If ngOnDestroy can be called I don't see why init can'tAdding to answer by @Sasxa,
In Injectables you can use class normally that is putting initial code in constructor instead of using ngOnInit(), it works fine.
Note: this answer applies only to Angular components and directives, NOT services.
I had this same issue when ngOnInit (and other lifecycle hooks) were not firing for my components, and most searches led me here.
The issue is that I was using the arrow function syntax (=>) like this:
class MyComponent implements OnInit { // Bad: do not use arrow function public ngOnInit = () => { console.log("ngOnInit"); } } Apparently that does not work in Angular 6. Using non-arrow function syntax fixes the issue:
class MyComponent implements OnInit { public ngOnInit() { console.log("ngOnInit"); } } 
ngOnInit.I had to call a function once my dataService was initialized, instead, I called it inside the constructor, that worked for me.
