Observe

Since iii 0.25 every function is observable. iii.observe(source, target, options?) connects a source function to a target function: each event of the source that passes the observer's filters invokes the target. It replaces registerTrigger, and an observe descriptor on registerFunction replaces registerTriggerType. Both old APIs still work in 0.25 (see Migrating from triggers).

Part	Fields	Notes
source (left side)	function_id, namespace?, args?, filters?, on?, capture?, deliver?	args only for owner-delivered functions. on (auto only): success (default), error, complete. capture (auto and obs.emit): default ['input', 'output', 'caller'], [] allowed. deliver: envelope (default), input, output
target (right side)	a registered function id (or { function_id, namespace })	No inline handler. The observer stays pending until the target is registered
options	id?, max_fires?, expires_in_ms?, max_in_flight?, metadata?	id defaults to a UUID kept across replays. metadata is the sidecar of every activation

The source namespace resolves like trigger(): the worker's namespace, except engine::* and configuration::*, which resolve in default.

Observe a function

Register the target first, then observe. This alerts on failed charges of 500 or more:

import { registerWorker, type Observed } from "iii-sdk";

const iii = registerWorker(process.env.III_URL ?? "ws://localhost:49134");

iii.registerFunction("alerts::payment-failed", async (event: Observed<{ amount: number }>) => {
  console.log(event.function_id, event.error?.code, event.input?.amount, event.caller?.worker_name);
  return null; // ignored for auto delivery
});