Observable way

import { Component } from '@angular/core';
import { FormGroup, FormBuilder }  from '@angular/forms';

@Component({
  selector: 'my-home',
  templateUrl: './home.component.html'
})
export class HomeComponent {
  userForm: FormGroup;

  constructor (formBuilder: FormBuilder) {
    this.userForm = formBuilder.group({
      name: '',
      email: '',
      address: formBuilder.group({
        country: '',
        city: '',
      })
    });
  }

  ngOnInit() {
    const nameControl = this.userForm.controls["name"];
    nameControl.valueChanges.subscribe(value => {
      if (value.trim() === '') {
        nameControl.setErrors({
          required: true
        });
      }
    });
  }

  onFormSubmitted(form) {
    console.log('form value:', form);
    // Rest of the logic here
  }
}