@sagentic-ai/sagentic-af / ReactiveAgent

ReactiveAgent<OptionsType, StateType, ReturnType>

ReactiveAgent is a base class for agents that are defined in terms of reactions to structured messages.

Extends

• BaseAgent<OptionsType, StateType, ReturnType>

Type parameters

• OptionsType extends AgentOptions

Options for the agent

• StateType

State of the agent

• ReturnType

Return type of the agent

Constructors

new ReactiveAgent(session, options)

new ReactiveAgent<OptionsType, StateType, ReturnType>(session, options): ReactiveAgent<OptionsType, StateType, ReturnType>

Create a new reactive agent.

Parameters

• session: Session

Session to use

• options: OptionsType

Options for the agent

Returns

ReactiveAgent<OptionsType, StateType, ReturnType>

Overrides

BaseAgent.constructor

Source

src/agents/reactive.ts:104

Properties

defaultReaction

defaultReaction: undefined | (s, m) => StateType = undefined;

Source

src/agents/reactive.ts:96

---

eatToolResults

eatToolResults: boolean = false;

Flag to indicate whether the tool results should be removed from threads after they were read

Inherited from

BaseAgent.eatToolResults

Source

src/agent.ts:111

---

expectsJSON

expectsJSON: boolean = true;

Flag to indicate whether the agent expects JSON output from the LLM

Overrides

BaseAgent.expectsJSON

Source

src/agents/reactive.ts:93

---

isActive

isActive: boolean = false;

Flag to indicate if the agent is active or not. Agent is only active during run

Inherited from

BaseAgent.isActive

Source

src/agent.ts:105

---

maxTokens?

optional maxTokens: number = undefined;

Maximum tokens to produce

Inherited from

BaseAgent.maxTokens

Source

src/agent.ts:120

---

metadata

metadata: Metadata;

Holds metadata of the object

Inherited from

BaseAgent.metadata

Source

src/agent.ts:87

---

model?

optional model: ModelType;

Model to use for the agent, can be undefined if the agent does not need to talk to any model.

Inherited from

BaseAgent.model

Source

src/agent.ts:96

---

options

options: OptionsType;

Options for the agent, use to pass custom data in constructor.

Inherited from

BaseAgent.options

Source

src/agent.ts:90

---

reactions

reactions: Reaction<any, StateType>[] = [];

Source

src/agents/reactive.ts:95

---

result?

optional result: ReturnType = undefined;

Result of the agent, obtained by calling finalize

Inherited from

BaseAgent.result

Source

src/agent.ts:102

---

rules

rules: string[];

Source

src/agents/reactive.ts:98

---

state?

optional state: StateType = undefined;

State of the agent, initial state is obtained by calling initialize

Inherited from

BaseAgent.state

Source

src/agent.ts:99

---

systemPrompt?

optional systemPrompt: string;

System prompt, can be undefined if the agent does not need one.

Inherited from

BaseAgent.systemPrompt

Source

src/agent.ts:93

---

temperature

temperature: number = 0.0;

Temperature to use with the LLM

Inherited from

BaseAgent.temperature

Source

src/agent.ts:117

---

thread

thread: Thread;

Source

src/agents/reactive.ts:92

---

tools

tools: Tool[] = [];

Tools for the agent to use

Inherited from

BaseAgent.tools

Source

src/agent.ts:108

---

captureRejectionSymbol

static readonly captureRejectionSymbol: typeof captureRejectionSymbol;

Value: Symbol.for('nodejs.rejection')

See how to write a custom rejection handler.

Since

v13.4.0, v12.16.0

Inherited from

BaseAgent.captureRejectionSymbol

Source

node_modules/@types/node/events.d.ts:402

---

captureRejections

static captureRejections: boolean;

Value: boolean

Change the default captureRejections option on all new EventEmitter objects.

Since

v13.4.0, v12.16.0

Inherited from

BaseAgent.captureRejections

Source

node_modules/@types/node/events.d.ts:409

---

defaultMaxListeners

static defaultMaxListeners: number;

By default, a maximum of 10 listeners can be registered for any single event. This limit can be changed for individual EventEmitter instances using the emitter.setMaxListeners(n) method. To change the default for allEventEmitter instances, the events.defaultMaxListenersproperty can be used. If this value is not a positive number, a RangeErroris thrown.

Take caution when setting the events.defaultMaxListeners because the change affects allEventEmitter instances, including those created before the change is made. However, calling emitter.setMaxListeners(n) still has precedence over events.defaultMaxListeners.

This is not a hard limit. The EventEmitter instance will allow more listeners to be added but will output a trace warning to stderr indicating that a "possible EventEmitter memory leak" has been detected. For any singleEventEmitter, the emitter.getMaxListeners() and emitter.setMaxListeners()methods can be used to temporarily avoid this warning:

import { EventEmitter } from "node:events";
const emitter = new EventEmitter();
emitter.setMaxListeners(emitter.getMaxListeners() + 1);
emitter.once("event", () => {
  // do stuff
  emitter.setMaxListeners(Math.max(emitter.getMaxListeners() - 1, 0));
});

The --trace-warnings command-line flag can be used to display the stack trace for such warnings.

The emitted warning can be inspected with process.on('warning') and will have the additional emitter, type, and count properties, referring to the event emitter instance, the event's name and the number of attached listeners, respectively. Its name property is set to 'MaxListenersExceededWarning'.

Since

v0.11.2

Inherited from

BaseAgent.defaultMaxListeners

Source

node_modules/@types/node/events.d.ts:446

---

errorMonitor

static readonly errorMonitor: typeof errorMonitor;

This symbol shall be used to install a listener for only monitoring 'error'events. Listeners installed using this symbol are called before the regular'error' listeners are called.

Installing a listener using this symbol does not change the behavior once an'error' event is emitted. Therefore, the process will still crash if no regular 'error' listener is installed.

Since

v13.6.0, v12.17.0

Inherited from

BaseAgent.errorMonitor

Source

node_modules/@types/node/events.d.ts:395

Accessors

modelDetails

get modelDetails(): undefined | ModelPricing

Model details

Returns

undefined | ModelPricing

Source

src/agent.ts:138

---

modelInvocationOptions

get modelInvocationOptions(): undefined | Partial<ChatCompletionCreateParamsNonStreaming>

Model invocation options that the agent uses. Contains tools to use and other options accepted by OpenAI.

Returns

undefined | Partial<ChatCompletionCreateParamsNonStreaming>

Source

src/agent.ts:344

---

parent

get parent(): Session

Parent of this object.

Throws

Error if parent is not set.

Returns

Session

Source

src/agent.ts:125

---

session

get session(): Session

Session that the agent belongs to, alias to parent

Returns

Session

Source

src/agent.ts:133

Methods

[captureRejectionSymbol]()?

optional [captureRejectionSymbol](
   error,
   event, ...
   args): void

Parameters

• error: Error

• event: string

• ...args: any[]

Returns

void

Inherited from

BaseAgent.[captureRejectionSymbol]

Source

node_modules/@types/node/events.d.ts:112

---

abandon()

abandon(child): void

Abandon a child object.

Parameters

• child: Thread

Returns

void

Inherited from

BaseAgent.abandon

Throws

Error throw if child object is not adopted.

Source

src/agent.ts:431

---

addListener()

addListener(eventName, listener): this

Alias for emitter.on(eventName, listener).

Parameters

• eventName: string | symbol

• listener

Returns

this

Inherited from

BaseAgent.addListener

Since

v0.1.26

Source

node_modules/@types/node/events.d.ts:545

---

adopt()

adopt(child): void

Adopt a child object, should.

Parameters

• child: Thread

Returns

void

Inherited from

BaseAgent.adopt

Throws

Error if child object is somebody's else or is already adopted.

Source

src/agent.ts:421

---

advance()

advance(thread): Promise<Thread>

Advances the thread by sending it to the model. This might take a while, as it waits for the model to respond. The thread is advanced mutably, so the same thread is returned. This essentially appends the model's response to the thread.

Parameters

• thread: Thread

the thread to advance

Returns

Promise<Thread>

the next thread

Inherited from

BaseAgent.advance

Source

src/agent.ts:261

---

conclude()

conclude(): void

Concludes the object. Finishes the timing object in metadata.

Returns

void

Inherited from

BaseAgent.conclude

Source

src/agent.ts:438

---

createThread()

createThread(): Thread

Creates a new thread for the agent and adopts it.

Returns

Thread

the new thread

Inherited from

BaseAgent.createThread

Source

src/agent.ts:248

---

describeTools()

describeTools(): ChatCompletionTool[]

Describes the tools that the agent uses.

Returns

ChatCompletionTool[]

the OpenAI schema for the tools that the agent can use

Inherited from

BaseAgent.describeTools

Source

src/agent.ts:336

---

emit()

emit<U>(event, ...args): boolean

Type parameters

• U extends keyof AgentEvents<StateType, ResultType>

Parameters

• event: U

• ...args: Parameters<AgentEvents<StateType, ReturnType>[U]>

Returns

boolean

Inherited from

BaseAgent.emit

Source

src/agent.ts:59

---

eventNames()

eventNames(): (string | symbol)[]

Returns an array listing the events for which the emitter has registered listeners. The values in the array are strings or Symbols.

import { EventEmitter } from "node:events";

const myEE = new EventEmitter();
myEE.on("foo", () => {});
myEE.on("bar", () => {});

const sym = Symbol("symbol");
myEE.on(sym, () => {});

console.log(myEE.eventNames());
// Prints: [ 'foo', 'bar', Symbol(symbol) ]

Returns

(string | symbol)[]

Inherited from

BaseAgent.eventNames

Since

v6.0.0

Source

node_modules/@types/node/events.d.ts:870

---

finalize()

finalize(state): Promise<ReturnType>

Finalizes the agent. Used to finalize the agent's work and obtain the final result. Implement this when extending the class.

Parameters

• state: StateType

the final state of the agent

Returns

Promise<ReturnType>

the final result of the agent

Overrides

BaseAgent.finalize

Source

src/agents/reactive.ts:115

---

getMaxListeners()

getMaxListeners(): number

Returns the current max listener value for the EventEmitter which is either set by emitter.setMaxListeners(n) or defaults to defaultMaxListeners.

Returns

number

Inherited from

BaseAgent.getMaxListeners

Since

v1.0.0

Source

node_modules/@types/node/events.d.ts:722

---

handleToolCalls()

handleToolCalls(thread): Promise<Thread>

Handles tool calls in a given thread by invoking the corresponding tool and appending the result to the thread. Resulting thread still needs to be completed using advance to obtain the assistant response.

Parameters

• thread: Thread

The thread containing the tool calls to be handled.

Returns

Promise<Thread>

A promise that resolves to the updated thread with the tool results appended.

Inherited from

BaseAgent.handleToolCalls

Remarks

This method is called by advance when the assistant returns tool calls.

Source

src/agent.ts:371

---

heartbeat()

heartbeat(): void

Notify session that the agent is still active. Use in long-running side-effects (e.g. tool invocations, long external requests, etc.) to prevent timeouts. This method is automatically called in step so you don't need to call it manually in most cases.

Returns

void

Inherited from

BaseAgent.heartbeat

Source

src/agent.ts:450

---

initialize()

initialize(options): Promise<StateType>

Initializes the agent. Used to set up the initial state of the agent. Is called before first invocation of step. Implement this when extending the class.

Parameters

• options: OptionsType

options for the agent

Returns

Promise<StateType>

the initial state of the agent

Overrides

BaseAgent.initialize

Source

src/agents/reactive.ts:109

---

input()

input(_options): Promise<StateType>

Transform the input into the initial agent state.

Parameters

• _options: OptionsType

Returns

Promise<StateType>

Initial state of the agent

Source

src/agents/reactive.ts:139

---

listenerCount()

listenerCount(eventName, listener?): number

Returns the number of listeners listening for the event named eventName. If listener is provided, it will return how many times the listener is found in the list of the listeners of the event.

Parameters

• eventName: string | symbol

The name of the event being listened for

• listener?: Function

The event handler function

Returns

number

Inherited from

BaseAgent.listenerCount

Since

v3.2.0

Source

node_modules/@types/node/events.d.ts:816

---

listeners()

listeners(eventName): Function[]

Returns a copy of the array of listeners for the event named eventName.

server.on("connection", (stream) => {
  console.log("someone connected!");
});
console.log(util.inspect(server.listeners("connection")));
// Prints: [ [Function] ]

Parameters

• eventName: string | symbol

Returns

Function[]

Inherited from

BaseAgent.listeners

Since

v0.1.26

Source

node_modules/@types/node/events.d.ts:735

---

notify()

notify(...stuff): undefined | number

Parameters

• ...stuff: any[]

Returns

undefined | number

Inherited from

BaseAgent.notify

Source

src/agent.ts:454

---

off()

off<U>(event, listener): this

Type parameters

• U extends keyof AgentEvents<StateType, ResultType>

Parameters

• event: U

• listener: AgentEvents<StateType, ReturnType>[U]

Returns

this

Inherited from

BaseAgent.off

Source

src/agent.ts:63

---

on()

on<U>(event, listener): this

Type parameters

• U extends keyof AgentEvents<StateType, ResultType>

Parameters

• event: U

• listener: AgentEvents<StateType, ReturnType>[U]

Returns

this

Inherited from

BaseAgent.on

Source

src/agent.ts:55

---

once()

once<U>(event, listener): this

Type parameters

• U extends keyof AgentEvents<StateType, ResultType>

Parameters

• event: U

• listener: AgentEvents<StateType, ReturnType>[U]

Returns

this

Inherited from

BaseAgent.once

Source

src/agent.ts:67

---

output()

output(_state): Promise<ReturnType>

Transform the final agent state into the output.

Parameters

• _state: StateType

Returns

Promise<ReturnType>

Output of the agent

Source

src/agents/reactive.ts:148

---

prependListener()

prependListener(eventName, listener): this

Adds the listener function to the beginning of the listeners array for the event named eventName. No checks are made to see if the listener has already been added. Multiple calls passing the same combination of eventNameand listener will result in the listener being added, and called, multiple times.

server.prependListener("connection", (stream) => {
  console.log("someone connected!");
});

Returns a reference to the EventEmitter, so that calls can be chained.

Parameters

• eventName: string | symbol

The name of the event.

• listener

The callback function

Returns

this

Inherited from

BaseAgent.prependListener

Since

v6.0.0

Source

node_modules/@types/node/events.d.ts:834

---

prependOnceListener()

prependOnceListener(eventName, listener): this

Adds a one-timelistener function for the event named eventName to the beginning of the listeners array. The next time eventName is triggered, this listener is removed, and then invoked.

server.prependOnceListener("connection", (stream) => {
  console.log("Ah, we have our first user!");
});

Returns a reference to the EventEmitter, so that calls can be chained.

Parameters

• eventName: string | symbol

The name of the event.

• listener

The callback function

Returns

this

Inherited from

BaseAgent.prependOnceListener

Since

v6.0.0

Source

node_modules/@types/node/events.d.ts:850

---

rawListeners()

rawListeners(eventName): Function[]

Returns a copy of the array of listeners for the event named eventName, including any wrappers (such as those created by .once()).

import { EventEmitter } from "node:events";
const emitter = new EventEmitter();
emitter.once("log", () => console.log("log once"));

// Returns a new Array with a function `onceWrapper` which has a property
// `listener` which contains the original listener bound above
const listeners = emitter.rawListeners("log");
const logFnWrapper = listeners[0];

// Logs "log once" to the console and does not unbind the `once` event
logFnWrapper.listener();

// Logs "log once" to the console and removes the listener
logFnWrapper();

emitter.on("log", () => console.log("log persistently"));
// Will return a new Array with a single function bound by `.on()` above
const newListeners = emitter.rawListeners("log");

// Logs "log persistently" twice
newListeners[0]();
emitter.emit("log");

Parameters

• eventName: string | symbol

Returns

Function[]

Inherited from

BaseAgent.rawListeners

Since

v9.4.0

Source

node_modules/@types/node/events.d.ts:766

---

removeAllListeners()

removeAllListeners(event?): this

Removes all listeners, or those of the specified eventName.

It is bad practice to remove listeners added elsewhere in the code, particularly when the EventEmitter instance was created by some other component or module (e.g. sockets or file streams).

Returns a reference to the EventEmitter, so that calls can be chained.

Parameters

• event?: string | symbol

Returns

this

Inherited from

BaseAgent.removeAllListeners

Since

v0.1.26

Source

node_modules/@types/node/events.d.ts:706

---

removeListener()

removeListener(eventName, listener): this

Removes the specified listener from the listener array for the event namedeventName.

const callback = (stream) => {
  console.log("someone connected!");
};
server.on("connection", callback);
// ...
server.removeListener("connection", callback);

removeListener() will remove, at most, one instance of a listener from the listener array. If any single listener has been added multiple times to the listener array for the specified eventName, then removeListener() must be called multiple times to remove each instance.

Once an event is emitted, all listeners attached to it at the time of emitting are called in order. This implies that anyremoveListener() or removeAllListeners() calls after emitting and before the last listener finishes execution will not remove them fromemit() in progress. Subsequent events behave as expected.

import { EventEmitter } from "node:events";
class MyEmitter extends EventEmitter {}
const myEmitter = new MyEmitter();

const callbackA = () => {
  console.log("A");
  myEmitter.removeListener("event", callbackB);
};

const callbackB = () => {
  console.log("B");
};

myEmitter.on("event", callbackA);

myEmitter.on("event", callbackB);

// callbackA removes listener callbackB but it will still be called.
// Internal listener array at time of emit [callbackA, callbackB]
myEmitter.emit("event");
// Prints:
//   A
//   B

// callbackB is now removed.
// Internal listener array [callbackA]
myEmitter.emit("event");
// Prints:
//   A

Because listeners are managed using an internal array, calling this will change the position indices of any listener registered after the listener being removed. This will not impact the order in which listeners are called, but it means that any copies of the listener array as returned by the emitter.listeners() method will need to be recreated.

When a single function has been added as a handler multiple times for a single event (as in the example below), removeListener() will remove the most recently added instance. In the example the once('ping')listener is removed:

import { EventEmitter } from "node:events";
const ee = new EventEmitter();

function pong() {
  console.log("pong");
}

ee.on("ping", pong);
ee.once("ping", pong);
ee.removeListener("ping", pong);

ee.emit("ping");
ee.emit("ping");

Returns a reference to the EventEmitter, so that calls can be chained.

Parameters

• eventName: string | symbol

• listener

Returns

this

Inherited from

BaseAgent.removeListener

Since

v0.1.26

Source

node_modules/@types/node/events.d.ts:690

---

respond()

respond(
   message,
   images?,
   options?): void

Parameters

• message: string

• images?: string[]

• options?

• options.detail?: "auto" | "high" | "low"

Returns

void

Source

src/agents/reactive.ts:119

---

run()

run(): Promise<ReturnType>

Starts the agent. Returns the final result when the agent is done.

Returns

Promise<ReturnType>

the final result of the agent's work

Inherited from

BaseAgent.run

Source

src/agent.ts:171

---

setMaxListeners()

setMaxListeners(n): this

By default EventEmitters will print a warning if more than 10 listeners are added for a particular event. This is a useful default that helps finding memory leaks. The emitter.setMaxListeners() method allows the limit to be modified for this specific EventEmitter instance. The value can be set toInfinity (or 0) to indicate an unlimited number of listeners.

Returns a reference to the EventEmitter, so that calls can be chained.

Parameters

• n: number

Returns

this

Inherited from

BaseAgent.setMaxListeners

Since

v0.3.5

Source

node_modules/@types/node/events.d.ts:716

---

spawnAgent()

spawnAgent<T>(constructor, options?): T

Create another agent within the session. It delegates to Session.spawnAgent in the session of this agent.

Type parameters

• T extends Agent

Parameters

• constructor: Constructor<T>

constructor of the agent to create

• options?: AgentOptions

options for the agent

Returns

T

Inherited from

BaseAgent.spawnAgent

Source

src/agent.ts:409

---

step()

step(state): Promise<StateType>

Steps the agent. Used to advance the agent's work. Is called repeatedly until stop is called. Implement this when extending the class.

Parameters

• state: StateType

the final state of the agent

Returns

Promise<StateType>

the next state of the agent

Overrides

BaseAgent.step

Source

src/agents/reactive.ts:152

---

stop()

stop(): void

Indicates that the agent should be stopped. Call only from step to finish agent's work.

Returns

void

Inherited from

BaseAgent.stop

Source

src/agent.ts:206

---

trace()

trace(...stuff): undefined | number

Parameters

• ...stuff: any[]

Returns

undefined | number

Inherited from

BaseAgent.trace

Source

src/agent.ts:466

---

addAbortListener()

Experimental

static addAbortListener(signal, resource): Disposable

Listens once to the abort event on the provided signal.

Listening to the abort event on abort signals is unsafe and may lead to resource leaks since another third party with the signal can call e.stopImmediatePropagation(). Unfortunately Node.js cannot change this since it would violate the web standard. Additionally, the original API makes it easy to forget to remove listeners.

This API allows safely using AbortSignals in Node.js APIs by solving these two issues by listening to the event such that stopImmediatePropagation does not prevent the listener from running.

Returns a disposable so that it may be unsubscribed from more easily.

import { addAbortListener } from "node:events";

function example(signal) {
  let disposable;
  try {
    signal.addEventListener("abort", (e) => e.stopImmediatePropagation());
    disposable = addAbortListener(signal, (e) => {
      // Do something when signal is aborted.
    });
  } finally {
    disposable?.[Symbol.dispose]();
  }
}

Parameters

• signal: AbortSignal

• resource

Returns

Disposable

Disposable that removes the abort listener.

Inherited from

BaseAgent.addAbortListener

Since

v20.5.0

Source

node_modules/@types/node/events.d.ts:387

---

getEventListeners()

static getEventListeners(emitter, name): Function[]

Returns a copy of the array of listeners for the event named eventName.

For EventEmitters this behaves exactly the same as calling .listeners on the emitter.

For EventTargets this is the only way to get the event listeners for the event target. This is useful for debugging and diagnostic purposes.

import { getEventListeners, EventEmitter } from "node:events";

{
  const ee = new EventEmitter();
  const listener = () => console.log("Events are fun");
  ee.on("foo", listener);
  console.log(getEventListeners(ee, "foo")); // [ [Function: listener] ]
}
{
  const et = new EventTarget();
  const listener = () => console.log("Events are fun");
  et.addEventListener("foo", listener);
  console.log(getEventListeners(et, "foo")); // [ [Function: listener] ]
}

Parameters

• emitter: EventEmitter | _DOMEventTarget

• name: string | symbol

Returns

Function[]

Inherited from

BaseAgent.getEventListeners

Since

v15.2.0, v14.17.0

Source

node_modules/@types/node/events.d.ts:308

---

getMaxListeners()

static getMaxListeners(emitter): number

Returns the currently set max amount of listeners.

For EventEmitters this behaves exactly the same as calling .getMaxListeners on the emitter.

For EventTargets this is the only way to get the max event listeners for the event target. If the number of event handlers on a single EventTarget exceeds the max set, the EventTarget will print a warning.

import { getMaxListeners, setMaxListeners, EventEmitter } from "node:events";

{
  const ee = new EventEmitter();
  console.log(getMaxListeners(ee)); // 10
  setMaxListeners(11, ee);
  console.log(getMaxListeners(ee)); // 11
}
{
  const et = new EventTarget();
  console.log(getMaxListeners(et)); // 10
  setMaxListeners(11, et);
  console.log(getMaxListeners(et)); // 11
}

Parameters

• emitter: EventEmitter | _DOMEventTarget

Returns

number

Inherited from

BaseAgent.getMaxListeners

Since

v19.9.0

Source

node_modules/@types/node/events.d.ts:337

---

listenerCount()

static listenerCount(emitter, eventName): number

A class method that returns the number of listeners for the given eventNameregistered on the given emitter.

import { EventEmitter, listenerCount } from "node:events";

const myEmitter = new EventEmitter();
myEmitter.on("event", () => {});
myEmitter.on("event", () => {});
console.log(listenerCount(myEmitter, "event"));
// Prints: 2

Parameters

• emitter: EventEmitter

The emitter to query

• eventName: string | symbol

The event name

Returns

number

Inherited from

BaseAgent.listenerCount

Since

v0.9.12

Deprecated

Since v3.2.0 - Use listenerCount instead.

Source

node_modules/@types/node/events.d.ts:280

---

on()

static on(
   emitter,
   eventName,
options?): AsyncIterableIterator<any>

import { on, EventEmitter } from "node:events";
import process from "node:process";

const ee = new EventEmitter();

// Emit later on
process.nextTick(() => {
  ee.emit("foo", "bar");
  ee.emit("foo", 42);
});

for await (const event of on(ee, "foo")) {
  // The execution of this inner block is synchronous and it
  // processes one event at a time (even with await). Do not use
  // if concurrent execution is required.
  console.log(event); // prints ['bar'] [42]
}
// Unreachable here

Returns an AsyncIterator that iterates eventName events. It will throw if the EventEmitter emits 'error'. It removes all listeners when exiting the loop. The value returned by each iteration is an array composed of the emitted event arguments.

An AbortSignal can be used to cancel waiting on events:

import { on, EventEmitter } from "node:events";
import process from "node:process";

const ac = new AbortController();

(async () => {
  const ee = new EventEmitter();

  // Emit later on
  process.nextTick(() => {
    ee.emit("foo", "bar");
    ee.emit("foo", 42);
  });

  for await (const event of on(ee, "foo", { signal: ac.signal })) {
    // The execution of this inner block is synchronous and it
    // processes one event at a time (even with await). Do not use
    // if concurrent execution is required.
    console.log(event); // prints ['bar'] [42]
  }
  // Unreachable here
})();

process.nextTick(() => ac.abort());

Parameters

• emitter: EventEmitter

• eventName: string

The name of the event being listened for

• options?: StaticEventEmitterOptions

Returns

AsyncIterableIterator<any>

that iterates eventName events emitted by the emitter

Inherited from

BaseAgent.on

Since

v13.6.0, v12.16.0

Source

node_modules/@types/node/events.d.ts:258

---

once()

once(emitter, eventName, options)

static once(
   emitter,
   eventName,
options?): Promise<any[]>

Creates a Promise that is fulfilled when the EventEmitter emits the given event or that is rejected if the EventEmitter emits 'error' while waiting. The Promise will resolve with an array of all the arguments emitted to the given event.

This method is intentionally generic and works with the web platform EventTarget interface, which has no special'error' event semantics and does not listen to the 'error' event.

import { once, EventEmitter } from "node:events";
import process from "node:process";

const ee = new EventEmitter();

process.nextTick(() => {
  ee.emit("myevent", 42);
});

const [value] = await once(ee, "myevent");
console.log(value);

const err = new Error("kaboom");
process.nextTick(() => {
  ee.emit("error", err);
});

try {
  await once(ee, "myevent");
} catch (err) {
  console.error("error happened", err);
}

The special handling of the 'error' event is only used when events.once()is used to wait for another event. If events.once() is used to wait for the 'error' event itself, then it is treated as any other kind of event without special handling:

import { EventEmitter, once } from "node:events";

const ee = new EventEmitter();

once(ee, "error")
  .then(([err]) => console.log("ok", err.message))
  .catch((err) => console.error("error", err.message));

ee.emit("error", new Error("boom"));

// Prints: ok boom

An AbortSignal can be used to cancel waiting for the event:

import { EventEmitter, once } from "node:events";

const ee = new EventEmitter();
const ac = new AbortController();

async function foo(emitter, event, signal) {
  try {
    await once(emitter, event, { signal });
    console.log("event emitted!");
  } catch (error) {
    if (error.name === "AbortError") {
      console.error("Waiting for the event was canceled!");
    } else {
      console.error("There was an error", error.message);
    }
  }
}

foo(ee, "foo", ac.signal);
ac.abort(); // Abort waiting for the event
ee.emit("foo"); // Prints: Waiting for the event was canceled!

Parameters

• emitter: _NodeEventTarget

• eventName: string | symbol

• options?: StaticEventEmitterOptions

Returns

Promise<any[]>

Inherited from

BaseAgent.once

Since

v11.13.0, v10.16.0

Source

node_modules/@types/node/events.d.ts:193

once(emitter, eventName, options)

static once(
   emitter,
   eventName,
options?): Promise<any[]>

Parameters

• emitter: _DOMEventTarget

• eventName: string

• options?: StaticEventEmitterOptions

Returns

Promise<any[]>

Inherited from

BaseAgent.once

Source

node_modules/@types/node/events.d.ts:198

---

setMaxListeners()

static setMaxListeners(n?, ...eventTargets?): void

import { setMaxListeners, EventEmitter } from "node:events";

const target = new EventTarget();
const emitter = new EventEmitter();

setMaxListeners(5, target, emitter);

Parameters

• n?: number

A non-negative number. The maximum number of listeners per EventTarget event.

• ...eventTargets?: (EventEmitter | _DOMEventTarget)[]

Returns

void

Inherited from

BaseAgent.setMaxListeners

Since

v15.4.0

Source

node_modules/@types/node/events.d.ts:352