change the code like this because after constructor() only the ngOnInit() gets called so the value is getting null

constructor(private router: Router) {
   this.name = this.router.getCurrentNavigation().extras.state.example;
}

You're calling the method getCurrentNavigation too late. The navigation has finished.

You need call the getCurrentNavigation method inside of the constructor:

constructor(private router: Router) {
    this.name = this.router.getCurrentNavigation().extras.state.someData;
}

Or if you want to access the navigation in ngOnInit you can do following:

ngOnInit() {
    this.name = history.state.someData;
}

work for me Ionic 4

• this.router.url => /app/menu/etc // current position

This happened to me because there was a promise (asynchronous process) in the Event of the NavigationEnd, before consuming the getCurrentNavigation().extras().state of the current state.

I moved the promise after and voila! It managed to get the data without first being cleaned.

For spec (tests), the getCurrentNavigation() on constructor don´t work, you have to use the history at ngOnInit() and mock values at history, for example:

beforeEach(() => {
    window.history.pushState({name: 'MyName', id: 1}, '', '');
}

Now your component can use this values on ngOnInit() and use on spec.:

ngOnInit(): void {
    console.log(history.state.name);
}