title: Firebase App named '[DEFAULT]' already exists & google firebase reference does not work on the server
body: <p>I followed all the steps for the server configuration in  <a href="https://firebase.google.com/docs/database/server/retrieve-data#section-start" rel="noreferrer">https://firebase.google.com/docs/database/server/retrieve-data#section-start</a>, but when I try to create the reference in the browser tells me that the application called [default] already exists. At that time if preiono F5 then tells me that there is "databaseUrl" I must make sure to provide that data when starting the application firebase.</p>
  
  <pre><code>var express = require('express');
  var router = express.Router();
  
  var firebase = require('firebase');
  
  /* GET home page. */
  router.get('/', function(req, res, next) {
  
    firebase.initializeApp({
      serviceAccount: "aaaabbbbcccc.json",
      databaseUrl: "https://xxxxxyyyyyzzzzz.firebaseio.com/" // &lt;&lt;&lt;&lt;--- it can not find
    });
  
    var db = firebase.database();   // &lt;&lt;&lt;&lt;---- Here is a problem
    var ref = db.ref('vistas/principal');
    ref.once('value', function(data){
  
      res.render('index', { title: 'Express' });
  
    });
  
  
  });
  
  module.exports = router;
  </code></pre>
  
  <p>I created other authorizations, other keys, etc. But nothing works. Thank you.</p>
  
  <p>Node -v = v4.2.6
  Firebase v3.x</p>
  
  <pre><code>FIREBASE FATAL ERROR: Can't determine Firebase Database URL. Be sure to include databaseURL option when calling firebase.intializeApp().
  
  Error: FIREBASE FATAL ERROR: Can't determine Firebase Database URL.  Be sure to include databaseURL option when calling firebase.intializeApp(). 
      at Error (native)
      at ad (c:\TsPrj\_pruebas\vistas-realtime-desde-firebase\node_modules\firebase\database-node.js:37:278)
      at Object.firebase.INTERNAL.registerService.Reference [as database] (c:\TsPrj\_pruebas\vistas-realtime-desde-firebase\node_modules\firebase\database-node.js:238:113)
      at O.u (c:\TsPrj\_pruebas\vistas-realtime-desde-firebase\node_modules\firebase\app-node.js:16:94)
      at Object.d [as database] (c:\TsPrj\_pruebas\vistas-realtime-desde-firebase\node_modules\firebase\app-node.js:18:182)
      at c:\TsPrj\_pruebas\vistas-realtime-desde-firebase\routes\index.js:14:21
      at Layer.handle [as handle_request] (c:\TsPrj\_pruebas\vistas-realtime-desde-firebase\node_modules\express\lib\router\layer.js:95:5)
      at next (c:\TsPrj\_pruebas\vistas-realtime-desde-firebase\node_modules\express\lib\router\route.js:131:13)
      at Route.dispatch (c:\TsPrj\_pruebas\vistas-realtime-desde-firebase\node_modules\express\lib\router\route.js:112:3)
      at Layer.handle [as handle_request] (c:\TsPrj\_pruebas\vistas-realtime-desde-firebase\node_modules\express\lib\router\layer.js:95:5)
  </code></pre>