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");
}
}