Why Map is not a Map when comming from a Map with ? definition

I have the following Angular code:

 var contactsKV: Map<string,string> = this.deviceContacts.contactList as Map<string,string>;
 var newContactsKV: Map<string,string> = new Map<string,string>;
 console.log("QQQ" + (contactsKV instanceof Map))
 console.log("ZZZ" + (newContactsKV instanceof Map))

Which throws:

QQQfalse
ZZZtrue

I would expect contactsKV to be of type Map. The only difference I can pinpoint in both variables is that contactList is defined optional:

export class Contact {  
  serialNumber?: string
  contactList?: Map<string,string>
}  

And the atribute with the Contact is declared like this:

export class DeviceContactsComponent implements OnInit {
  @Input() viewMode = true;  
  @Input() deviceContacts: Contact= {};//Neither works if I remove '= {}'

Any ideas on why Angular would do this? I need to use Map functions like delete() but they are not recognized in contactsKV as the type seems to be something else.

While both empty object ({}) and Map are dictionnaries, {} is not a Map.

If you want an empty map create a new one : new Map<string,string>;.

Edit: Seems like you were passing an object in input that was not a map !