Event Handlers

Overview

Events are the primary way your app receives data from the glasses. All event handlers are accessed through session.events.

Available Events

Transcription Events

// Default language (en-US)
session.events.onTranscription((data) => {
  console.log(`Text: ${data.text}`);
  console.log(`Final: ${data.isFinal}`);
  console.log(`Language: ${data.transcribeLanguage}`);
});

// Specific language
session.events.onTranscriptionForLanguage('es-ES', (data) => {
  console.log(`Spanish text: ${data.text}`);
});

TranscriptionData fields

text: The transcribed text
isFinal: Whether this is a final or interim result
transcribeLanguage: Language code (e.g., ‘en-US’)
startTime: Timestamp when speech started
endTime: Timestamp when speech ended
confidence: Confidence score (0-1)
provider: Transcription provider used

Button Events

session.events.onButtonPress((data) => {
  console.log(`Button: ${data.buttonId}`);
  console.log(`Type: ${data.pressType}`);
});

ButtonPress fields

buttonId: Button identifier (e.g., ‘main’)
pressType: ‘short’ or ‘long’

Head Position Events

session.events.onHeadPosition((data) => {
  if (data.position === 'up') {
    console.log('User looked up');
  } else if (data.position === 'down') {
    console.log('User looked down');
  }
});

Photo Events

session.events.onPhotoTaken((data) => {
  console.log(`Photo received: ${data.mimeType}`);
  // data.photoData is an ArrayBuffer
  processPhoto(data.photoData);
});

Location Events

// First subscribe to location updates
session.location.subscribeToStream({}, (data) => {
  console.log(`Location: ${data.lat}, ${data.lng}`);
  if (data.accuracy) {
    console.log(`Accuracy: ${data.accuracy} meters`);
  }
});

Phone Notifications

session.events.onPhoneNotifications((notifications) => {
  notifications.forEach(notification => {
    console.log(`${notification.app}: ${notification.title}`);
    console.log(`Content: ${notification.content}`);
  });
});

Connection Events

// When connection is lost
session.events.onDisconnected(() => {
  console.log('Connection lost');
});

// When connection is restored
session.events.onReconnected(() => {
  console.log('Connection restored');
});

// When session starts
session.events.onConnected((settings) => {
  console.log('Connected with settings:', settings);
});

// When errors occur
session.events.onError((error) => {
  console.error('Session error:', error);
});

Event Patterns

Debouncing Events

let timeout: NodeJS.Timeout;

session.events.onTranscription((data) => {
  clearTimeout(timeout);
  
  // Wait for user to stop speaking
  timeout = setTimeout(() => {
    processCompleteUtterance(data.text);
  }, 1000);
});

State Machines

enum State {
  IDLE,
  LISTENING,
  PROCESSING
}

let currentState = State.IDLE;

session.events.onButtonPress((data) => {
  switch (currentState) {
    case State.IDLE:
      currentState = State.LISTENING;
      session.layouts.showTextWall('Listening...');
      break;
      
    case State.LISTENING:
      currentState = State.PROCESSING;
      session.layouts.showTextWall('Processing...');
      processInput();
      break;
  }
});

Event Filtering

// Only respond to specific phrases
session.events.onTranscription((data) => {
  if (!data.isFinal) return; // Skip interim results
  
  const keywords = ['weather', 'time', 'news'];
  const hasKeyword = keywords.some(word => 
    data.text.toLowerCase().includes(word)
  );
  
  if (hasKeyword) {
    handleCommand(data.text);
  }
});

Multi-User Events

For apps that support multiple users:

// Listen for messages from other users
session.events.onAppMessage((message) => {
  console.log(`From ${message.senderUserId}: ${message.payload}`);
});

// User joined
session.events.onAppUserJoined((userId) => {
  console.log(`${userId} joined`);
});

// User left
session.events.onAppUserLeft((userId) => {
  console.log(`${userId} left`);
});

Best Practices

Clean up event handlers

Event handlers are automatically cleaned up when the session ends, but you can manually remove them:

const cleanup = session.events.onTranscription(handler);
// Later...
cleanup(); // Remove this handler

Handle errors gracefully

session.events.onError((error) => {
  console.error('Session error:', error);
  // Show user-friendly message
  session.layouts.showTextWall('Something went wrong. Please try again.');
});

Combine multiple events

let lastTranscript = '';
let lastButtonPress = Date.now();

session.events.onTranscription((data) => {
  lastTranscript = data.text;
});

session.events.onButtonPress((data) => {
  const timeSinceLastPress = Date.now() - lastButtonPress;
  if (timeSinceLastPress < 500) {
    // Double press detected
    processCommand(lastTranscript);
  }
  lastButtonPress = Date.now();
});

Performance Tips

Filter events early: Return early from handlers if the event isn’t relevant
Debounce rapid events: Use timeouts to batch rapid events
Avoid blocking operations: Use async/await for long-running tasks
Clean up resources: Remove handlers and clear timers when done

Getting Started

Cloud Overview

Cloud Architecture

SDK Reference

Development

Overview

Available Events

Transcription Events

TranscriptionData fields

Button Events

ButtonPress fields

Head Position Events

Photo Events

Location Events

Phone Notifications

Connection Events

Event Patterns

Debouncing Events

State Machines

Event Filtering

Multi-User Events

Best Practices

Performance Tips

​Overview

​Available Events

​Transcription Events

TranscriptionData fields

​Button Events

ButtonPress fields

​Head Position Events

​Photo Events

​Location Events

​Phone Notifications

​Connection Events

​Event Patterns

​Debouncing Events

​State Machines

​Event Filtering

​Multi-User Events

​Best Practices

​Performance Tips

Overview

Available Events

Transcription Events

Button Events

Head Position Events

Photo Events

Location Events

Phone Notifications

Connection Events

Event Patterns

Debouncing Events

State Machines

Event Filtering

Multi-User Events

Best Practices

Performance Tips