This program uses limbo-wasm to create an in-memory SQLite database that tracks and logs changes to a users table using triggers and a polling listener.

limbo.ts

import { Database } from 'limbo-wasm';

// Initialize Limbo database in memory
const db = new Database(':memory:');

// Function to initialize the database with error handling
function initializeDatabase() {
  try {
    db.exec(`
      CREATE TABLE IF NOT EXISTS users (id INTEGER PRIMARY KEY AUTOINCREMENT, name TEXT);
      CREATE TABLE IF NOT EXISTS change_log (
        id INTEGER PRIMARY KEY AUTOINCREMENT,
        table_name TEXT,
        rowid INTEGER,
        event_type TEXT,
        ts INTEGER
      );
      CREATE TRIGGER IF NOT EXISTS user_insert AFTER INSERT ON users
      BEGIN
        INSERT INTO change_log (table_name, rowid, event_type, ts)
        VALUES ('users', NEW.id, 'INSERT', strftime('%s', 'now'));
      END;
      CREATE TRIGGER IF NOT EXISTS user_update AFTER UPDATE ON users
      BEGIN
        INSERT INTO change_log (table_name, rowid, event_type, ts)
        VALUES ('users', NEW.id, 'UPDATE', strftime('%s', 'now'));
      END;
      CREATE TRIGGER IF NOT EXISTS user_delete AFTER DELETE ON users
      BEGIN
        INSERT INTO change_log (table_name, rowid, event_type, ts)
        VALUES ('users', OLD.id, 'DELETE', strftime('%s', 'now'));
      END;
    `);
    console.log('Database schema initialized successfully');

    // Verify tables exist
    const tables = db.prepare("SELECT name FROM sqlite_master WHERE type='table'").all();
    console.log('Tables in database:', tables);
  } catch (e) {
    console.error('Failed to initialize database:', e);
    process.exit(1);
  }
}

// Polling function to detect changes
let lastId = 0;
function startChangeListener() {
  console.log('Starting change listener...');
  try {
    setInterval(() => {
      const stmt = db.prepare(
        'SELECT * FROM change_log WHERE id > ? AND table_name = "users" ORDER BY id DESC LIMIT 1'
      );
      const changes = stmt.all();
      if (changes.length > 0) {
        const change = changes[0];
        console.log(
          `[Change Detected] Event: ${change.event_type}, RowID: ${change.rowid}, Timestamp: ${change.ts}`
        );
        lastId = change.id;
      }
    }, 500); // Poll every 500ms
  } catch (e) {
    console.error('Error in change listener:', e);
  }
}

// Simulate slow data population
function startDataPopulation() {
  console.log('Starting data population...');
  let counter = 1;
  setInterval(() => {
    try {
      if (counter <= 5) {
        db.exec(`INSERT INTO users (name) VALUES ('User-${counter}')`);
        console.log(`Inserted User-${counter}`);
      } else if (counter === 6) {
        db.exec(`UPDATE users SET name = 'Updated-User-1' WHERE id = 1`);
        console.log('Updated User-1');
      } else if (counter === 7) {
        db.exec(`DELETE FROM users WHERE id = 2`);
        console.log('Deleted User-2');
      }
      counter++;
    } catch (e) {
      console.error('Error in data population:', e);
    }
  }, 1000); // Insert/update/delete every 1 second
}

// Main execution
console.log('Main process starting...');
initializeDatabase();

// Start listener and population after a short delay to ensure schema is ready
setTimeout(() => {
  startChangeListener();
  startDataPopulation();
}, 100); // 100ms delay

// Keep Bun alive
setInterval(() => {}, 1000);

// Cleanup on exit
process.on('SIGINT', () => {
  db.free();
  console.log('Database closed. Exiting...');
  process.exit(0);
});

packages.json

{
  "dependencies": {
    "limbo-wasm": "^0.0.14"
  },
  "devDependencies": {
    "@types/bun": "^1.2.2"
  }
}