/** Get the current account */
public currentAccount(): Observable<string | Error> {
  if (this.web3.eth.defaultAccount) {
    return of(this.web3.eth.defaultAccount);
  } else {
    return this.getAccounts().pipe(
      tap((accounts: string[]) => {
        if (accounts.length === 0) { throw new Error(‘No accounts available’); }
      }),
      map((accounts: string[]) => accounts[0]),
      tap((account: string) => this.web3.eth.defaultAccount = account),
      catchError((err: Error) => of(err))
    );
  }
}