node:child_process

A WebAssembly guest cannot spawn a process itself. When bundled source imports node:child_process, Jco ensures that the selected world declares the dedicated interface:

world app {
  import jco:node/child-process@0.1.0;
  // component imports and exports...
}

If the selected world does not already contain the import, Jco edits its .wit file in place, adds a comment identifying the generated line, installs the interface definition under deps/jco-node-0.1.0, and prints a CLI warning naming the changed files. This makes the capability change visible in the application’s source control. --world is honored when a package defines multiple worlds, and repeated componentization does not add duplicate imports or dependencies.

The interface definition also ships in jco-std under wit/node-0.1.0. Declaring or generating the import does not grant host access: Jco’s default transpilation map uses a provider that throws ERR_JCO_CHILD_PROCESS_ADAPTER_REQUIRED. An application must make the security decision explicitly, for example by mapping the Node host provider:

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

That produces the call path guest node:child_process → WIT capability → host adapter → Node node:child_process.

The current interface supports spawnSync, execFileSync, and execSync, including buffered input/output, encoding, cwd, environment, shell, stdio, timeout, signal, identity, and Windows options. spawn, callback-based exec and execFile, ChildProcess, and fork/IPC are present but throw ERR_JCO_UNSUPPORTED_NODE_API. A synchronous WIT function cannot faithfully carry Node callbacks, lifecycle events, or interactive streams; those APIs stay explicitly unavailable until the capability grows an asynchronous resource and stream model.