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Overview

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

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Available Events

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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

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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’

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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');
  }
});

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Photo Events

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

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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`);
  }
});

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Phone Notifications

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

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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);
});

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Event Patterns

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Debouncing Events

let timeout: NodeJS.Timeout;

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

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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;
  }
});

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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);
  }
});

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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`);
});

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Best Practices

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

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

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();
});

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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