node:console

Writing to a console is a host capability, not a portable one: a component has no stdout of its own. node:console therefore resolves against jco:node/console@0.1.0, which an application must provide.

It is denied by default. Transpiling maps the capability to jco-std’s deny host unless told otherwise, and every call – write, isTerminal, colorDepth – throws ERR_JCO_CONSOLE_ADAPTER_REQUIRED. That is deliberate: a component that silently discarded its output would be harder to diagnose than one that says the capability is missing.

To grant it, map the interface to a provider. jco-std ships one for Node, which writes through to the real process.stdout/process.stderr and reports their TTY status and color depth:

jco transpile component.wasm \
  --map 'jco:node/console@0.1.0=@bytecodealliance/jco-std/wasi/0.2.x/node/24.x.x/console/host/node'

Formatting is done in the guest – Console, the log/warn/error family, group indentation, count, time, table and dir all run guest-side, and only the finished string crosses the boundary.