The 'jsrsasign' (RSA-Sign JavaScript Library) is an opensource free cryptography library supporting RSA/RSAPSS/ECDSA/DSA signing/validation, ASN.1, PKCS#1/5/8 private/public key, X.509 certificate, CRL, OCSP, CMS SignedData, TimeStamp, CAdES and JSON Web Signature/Token in pure JavaScript.
I'm sorry but there is no plan to support brainpool or other curves at this stage. EdDSA support will be required than other curves. Of course PR request will be welcomed as always.
I need for a ecdsa project the support for brainpool curves like brainpoolP384r1.