Question about parsing x509 extensions within a parsed Certificate

[MasterKale]

I'm trying to migrate more of my code over to asn1-schema but I'm stumped about how to take an extension out of an x.509 Certificate instance and then parse it through an extension schema.

After running my leaf cert through AsnParser.parse(leafCertBuffer, Certificate), I'm able to view the expected extensions:

Extensions(2) [
  Extension {
    extnID: '1.3.6.1.4.1.45724.2.1.1',
    critical: false,
    extnValue: OctetString {
      buffer: ArrayBuffer { [Uint8Contents]: <03 02 05 20>, byteLength: 4 }
    }
  },
  Extension {
    extnID: '2.5.29.19',
    critical: true,
    extnValue: OctetString {
      buffer: ArrayBuffer { [Uint8Contents]: <30 03 01 01 00>, byteLength: 5 }
    }
  }
]

What I want to do is then take that '2.5.29.19' (BasicConstraints) extension and parse it so I can more easily access its cA attribute. I tried this but of course the types didn't match:

if (ext.extnID === id_ce_basicConstraints) {
  console.log(AsnParser.fromASN(ext, BasicConstraints)); // No good, ext isn't a Buffer
}

Is there a clean way to further parse something that's within a parsed asn.1 schema? Thank you in advance for shining a light on this more advanced use case 😄

[MasterKale]

I figured it out, turns out I could just parse ext.extnValue:

if (ext.extnID === id_ce_basicConstraints) {
  console.log(AsnParser.parse(ext.extnValue, BasicConstraints));
}