dgram.Socket.connectSync

The synchronous counterpart of socket.connect(). For a UDP socket connect(2) only records the default peer address and is a local, non-blocking system call, so the association is performed inline. Any error raised by the call itself (for example EAFNOSUPPORT for a mismatched address family) is thrown synchronously rather than reported via the 'error' event. Because connect(2) does not probe reachability, errors such as ECONNREFUSED are still surfaced asynchronously on a later send or receive, exactly as for socket.connect():

const dgram = require('node:dgram');

const socket = dgram.createSocket('udp4');
socket.connectSync(41234, '127.0.0.1');
console.log(socket.remoteAddress()); // { address: '127.0.0.1', family: 'IPv4', port: 41234 }

If the socket is still unbound it is bound synchronously first. After connectSync() returns, socket.remoteAddress() is valid synchronously and the 'connect' event is emitted on the next tick. Trying to call connectSync() on an already connected socket throws an ERR_SOCKET_DGRAM_IS_CONNECTED exception, and calling it while an asynchronous [socket.bind()][] is still in progress throws an ERR_SOCKET_ALREADY_BOUND exception.

address must be a numeric IP literal; connectSync() never performs DNS resolution (asynchronous name resolution being the only genuinely blocking part of connecting).