node:net

node:net implements Node 24.19’s 18-export module surface over Preview 2 wasi:sockets. It includes TCP Socket and Server, BoundSocket, SocketAddress, BlockList, IP-family predicates, overload normalization, and the auto-family defaults. connect and createConnection are the same function, and Socket and Stream are the same constructor, as in Node.

import { connect, createServer } from 'node:net';

createServer((socket) => socket.end('hello')).listen(8080, '127.0.0.1');

connect(8080, '127.0.0.1').setEncoding('utf8').on('data', console.log);

Jco injects only the selected world’s Preview 2 DNS, TCP, stream, and pollable interfaces and their standard WIT packages. QuickJS worlds use 0.2.12; StarlingMonkey worlds can use 0.2.10. There is no Jco-specific network host interface and no bare net alias.

Preview 2 has no Unix-domain sockets, Windows named pipes, OS file descriptors, libuv handles, TCP reset, IP type-of-service, or custom JavaScript DNS callback. Those operations throw ERR_JCO_UNSUPPORTED_NODE_API. Address attempts are sequential rather than reproducing Node’s exact Happy Eyeballs timing. Socket objects provide the common readable/writable methods and events but do not yet inherit from classic node:stream.Duplex, because Jco does not have a faithful classic stream core.

Reads support Node string encodings, buffered read(), and async iteration. Writable operations complete through blocking WASI writes and do not yet provide classic stream backpressure. setNoDelay(), ref(), and unref() preserve the callable surface but cannot control the host’s TCP_NODELAY or event-loop references. Nonzero socket timeouts require an engine with JavaScript timers; engines without them reject setTimeout() explicitly. The deprecated bufferSize getter throws the Jco deprecated-API error; use writableLength instead.

Half-close depends on the host honoring WASI’s directional shutdown. The Preview 2 Node host shim 0.22.0 currently closes both directions; applications using that host should let the peer finish its response before closing the socket’s writable side.