Firebase

import db from '../../lib/db-admin';

export default (req, res) => {
  if (!req.query.id) {
    return res.status(400).json({
      error: 'Missing "id" query parameter'
    });
  }

  const ref = db.ref('table').child(req.query.id);

  return ref.once('value', (snapshot) => {
    res.status(200).json({
      total: snapshot.val()
    });
  });
};

// lib/db-admin.js

const admin = require('firebase-admin');

try {
  admin.initializeApp({
    credential: admin.credential.cert({
      client_email: process.env.FIREBASE_CLIENT_EMAIL,
      private_key: process.env.FIREBASE_PRIVATE_KEY,
      project_id: 'your-project-id'
    }),
    databaseURL: 'https://your-project-id.firebaseio.com'
  });
} catch (error) {
  /*
   * We skip the "already exists" message which is
   * not an actual error when we're hot-reloading.
   */
  if (!/already exists/u.test(error.message)) {
    console.error('Firebase admin initialization error', error.stack);
  }
}

module.exports = admin.database();