app.component.ts

@Component({
  selector: 'app-root',
  templateUrl: './app.component.html',
  styleUrls: ['./app.component.scss']
})
export class AppComponent {

  uploadProgress: Observable<number>;

  uploadURL: Observable<string>;

  constructor(private _storage: AngularFireStorage) { }

  upload(event) {
    // Get input file
    const file = event.target.files[0];

    // Generate a random ID
    const randomId = Math.random().toString(36).substring(2);
    console.log(randomId);
    const filepath = `images/${randomId}`;

    const fileRef = this._storage.ref(filepath);

    // Upload image
    const task = this._storage.upload(filepath, file);

    // Observe percentage changes
    this.uploadProgress = task.percentageChanges();

    // Get notified when the download URL is available
    task.snapshotChanges().pipe(
      finalize(() => this.uploadURL = fileRef.getDownloadURL())
    ).subscribe();
  }

}