Reactive Forms - mark fields as touched

From Angular 8 you can simply use

this.form.markAllAsTouched();

To mark a control and it's descendant controls as touched.

AbstractControl doc

The following function recurses through controls in a form group and gently touches them. Because the control's field is an object, the code call Object.values() on the form group's control field.

      /**
       * Marks all controls in a form group as touched
       * @param formGroup - The form group to touch
       */
      private markFormGroupTouched(formGroup: FormGroup) {
        (<any>Object).values(formGroup.controls).forEach(control => {
          control.markAsTouched();
    
          if (control.controls) {
            this.markFormGroupTouched(control);
          }
        });
      }