Implementation:Openai Openai node EventEmitter On

Knowledge Sources	openai-node OpenAI Realtime API
Domains	Realtime, Event_Driven_Architecture
Last Updated	2026-02-15 00:00 GMT

Overview

Concrete tool for registering typed event listeners on Realtime API connections provided by the openai-node SDK.

Description

The EventEmitter class provides a custom typed event emitter (NOT Node.js EventEmitter) with on(), off(), and once() methods. The Realtime API connections inherit from OpenAIRealtimeEmitter which extends this EventEmitter with Realtime-specific event types.

Key server events include: response.text.delta, response.audio.delta, response.audio_transcript.delta, response.function_call_arguments.delta, response.done, error, session.created, session.updated.

Usage

Use rt.on(eventName, callback) to register event listeners. Use rt.off(eventName, callback) to remove listeners. Use rt.once(eventName, callback) for one-time listeners.

Code Reference

Source Location

• Repository: openai-node
• File: src/lib/EventEmitter.ts
• Lines: L12-98 (EventEmitter class), L24-29 (on method), L38-44 (off method), L51-56 (once method)

Signature

export class EventEmitter<EventTypes extends Record<string, (...args: any[]) => void>> {
  on<Event extends keyof EventTypes>(
    event: Event,
    listener: EventTypes[Event],
  ): this;

  off<Event extends keyof EventTypes>(
    event: Event,
    listener: EventTypes[Event],
  ): this;

  once<Event extends keyof EventTypes>(
    event: Event,
    listener: EventTypes[Event],
  ): this;
}

Import

// EventEmitter is used internally; access via rt.on(), rt.off(), rt.once()

I/O Contract

Inputs

Name	Type	Required	Description
event	keyof EventTypes	Yes	Event name (e.g., 'response.text.delta', 'error')
listener	Function	Yes	Callback function receiving the typed event payload

Outputs

Name	Type	Description
this	EventEmitter	Returns self for chaining
(callback)	void	Listener is invoked with typed event payload when event occurs

Usage Examples

import { OpenAIRealtimeWS } from 'openai/realtime/ws';

const rt = await OpenAIRealtimeWS.create(client, {
  model: 'gpt-4o-realtime-preview',
});

// Handle text deltas
rt.on('response.text.delta', (event) => {
  process.stdout.write(event.delta);
});

// Handle audio transcript
rt.on('response.audio_transcript.delta', (event) => {
  process.stdout.write(event.delta);
});

// Handle completion
rt.on('response.done', (event) => {
  console.log('\nResponse complete');
});

// Handle errors
rt.on('error', (event) => {
  console.error('Error:', event.error.message);
});

// One-time session setup
rt.once('session.created', () => {
  console.log('Connected to Realtime API');
});

Related Pages

Implements Principle

• Principle:Openai_Openai_node_Realtime_Event_Handling

Requires Environment

• Environment:Openai_Openai_node_WebSocket_Dependency