Although CBOR is supported by all main-stream browsers (for WebAuthn), there is AFAIK still no public API. Something along these lines seems possible: https://github.com/cyberphone/CBOR.js#cborjs
One of the core ideas behind this particular take on the matter is defining a CBOR profile that could be adopted by other software platforms as well in order to avoid the chaos with JSON where Oracle and Microsoft use different approaches for encoding integers outside of Number.