BigInt not supported

require('msgpack5')().encode({a: 10n})
Uncaught Error: not implemented yet

I am a bit surprised that it isn't possible to write a decoder for this. I tried, but I get the same error, since msgpack5 never seems to try to get the value converted:

const m = require('msgpack5')()
m.registerEncoder((t) => (t instanceof BigInt), t => t.toString(10))
m..encode({a: 10n})
Uncaught Error: not implemented yet

Start by reproducing the issue with msgpack5().encode({a: 10n}) and compare it with the registerEncoder attempt shown in the report. Trace how BigInt values reach the encoder and determine the intended encoded and decoded representation; done means BigInt values no longer raise the reported error and the behavior is covered by tests.