Subscribe to a remote producer (TypeScript)¶

client.subscribe(path, handler) writes a SUBSCRIBER into the producer’s :subscribers[], and every later write to the producer is delivered to the handler.

The node on the other end is stand-in-node.mjs, an in-memory stand-in. The TypeScript packages have no node of their own, and the stand-in lets the example run with no C++ build. Against a real node the client code is unchanged.

What to notice¶

Two clients, one node. The consumer subscribes and a second client writes. The deliveries arrive in write order.
unsubscribe() is a local detach. It stops the handler firing; it does not clear the remote slot.
The handler is registered before the ack. A producer may deliver before its subscribe reply arrives, and the client does not drop that delivery.

Source¶

// SPDX-License-Identifier: Apache-2.0
// SPDX-FileCopyrightText: Copyright 2026 avatarsd LLC

/**
 * @file
 * @brief One concept: subscribe to a remote producer. Subscribing is itself a write —
 * a SUBSCRIBER into `/sensor/temp:subscribers[]` — and each later write to the producer
 * arrives as a delivery to the handler.
 *
 * Run: `node examples/subscribe.mjs` (from `bindings/typescript/`, after `npm run build`).
 */

import assert from 'node:assert/strict';
import { LibtracerClient, encodeValue } from '@avatarsd-llc/libtracer-client';
import { standInNode } from './stand-in-node.mjs';

const node = standInNode();
const consumer = new LibtracerClient(node.loopback());
const producer = new LibtracerClient(node.loopback());

// The handler fires inline, once per delivered VALUE.
const seen = [];
const unsubscribe = await consumer.subscribe('/sensor/temp', (value) => seen.push(value[0]));
console.log('subscribed to /sensor/temp');

// Two writes by another client -> two deliveries, in order.
await producer.write('/sensor/temp', encodeValue(Uint8Array.of(20)));
await producer.write('/sensor/temp', encodeValue(Uint8Array.of(21)));
assert.deepEqual(seen, [20, 21]);
console.log(`delivered: ${seen.join(', ')}`);

// unsubscribe() is a local detach: the handler stops firing.
unsubscribe();
await producer.write('/sensor/temp', encodeValue(Uint8Array.of(22)));
assert.deepEqual(seen, [20, 21]);
console.log('after unsubscribe: nothing more delivered');

Run it from bindings/typescript/, after npm ci && npm run build:

$ node examples/subscribe.mjs