How to use the ecdsa-sig-formatter.joseToDer function in ecdsa-sig-formatter

static loadSignature(joseSignature: string | Buffer) {
    // create and return the DER-formatted signature buffer
    return joseToDer(joseSignature, 'ES256')
  }

return function verify(thing, signature, publicKey) {
    signature = formatEcdsa.joseToDer(signature, 'ES' + bits).toString('base64');
    var result = inner(thing, signature, publicKey);
    return result;
  };
}

return function verify(thing, signature, publicKey) {
    signature = formatEcdsa.joseToDer(signature, 'ES' + bits).toString('base64');
    var result = inner(thing, signature, publicKey);
    return result;
  };
}

var verified, digest;

  if (cryptoAlgName === 'none') {
    verified = true;
  } else if (signingType === 'hmac') {
    digest = crypto.createHmac(cryptoAlgName, this.signingKey)
      .update(digstInput)
      .digest('base64');
    verified = signature === digest;
  } else {
    var unescapedSignature;
    var signatureType = undefined;

    if (helpers.isECDSA(header.alg)) {
      try {
        unescapedSignature = ecdsaSigFormatter.joseToDer(signature, header.alg);
      } catch (err) {
        return done(new errors.SignatureMismatchJwtParseError(jwtString, header, body, err));
      }
    } else {
      signatureType = 'base64';
      unescapedSignature = helpers.base64urlUnescape(signature);
    }

    verified = crypto.createVerify(cryptoAlgName)
      .update(digstInput)
      .verify(this.signingKey, unescapedSignature, signatureType);
  }

  var newJwt = new Jwt(body, false);

  newJwt.toString = function () {