AngularFire2 - Firebase Storage getDownloadURL() - How to return Firestore's URL

I've been going through the angularfire2 documentation to retrieve downloadURl from storage. I hope something simple is missing here.

The documentation states:

@Component({
  selector: 'app-root',
  template: `<img [src]="profileUrl | async" />`
})
 export class AppComponent {
   profileUrl: Observable<string | null>;
   constructor(private storage: AngularFireStorage) {
   const ref = this.storage.ref('users/davideast.jpg');
   this.profileUrl = ref.getDownloadURL();
 }
}

However, once I have uploaded the image, I want to return the download url as a string to upload to firestore. I need download URL for external service.

my function

uploadImage(base64data) {

  const filePath = (`myURL/photo.jpg`);
  const storageRef = firebase.storage().ref();

  var metadata = {
    contentType: 'image',
    cacheControl: "public, max-age=31536000",
  };

  const ref = this.storage.ref(filePath);
  const task = ref.putString(base64data, 'data_url', metadata).then(() => {

    var downloadURL = ref.getDownloadURL();

  })

}

This uploads the image perfectly. However, I want to write the download URL to firestore. When the console logs my "downloadURL" variable, I get the following:

PromiseObservable {_isScalar: no, promise: y, scheduler: undefined}

The download is inside an observable promise. How can I get only the download URL string as a variable? Once there, I can sort out the Firestore update.