Error: No Firebase App '[DEFAULT]' has been created
<p>I'm using Ionic2 and when I go to localhost:8100 (after doing <code>ionic serve</code>) I receive the error you can see in the following image. </p>

<p><a href="https://i.stack.imgur.com/ddJDN.png" rel="noreferrer"><img src="https://i.stack.imgur.com/ddJDN.png" alt="enter image description here"></a></p>

<p><strong>app.component.ts</strong> looks like this:</p>

<pre><code>import firebase from 'firebase';
import { Component } from '@angular/core';
import { Platform } from 'ionic-angular';
import { StatusBar } from 'ionic-native';
import { HomePage } from '../pages/home/home';

@Component({
  template: `&lt;ion-nav [root]="rootPage"&gt;&lt;/ion-nav&gt;`
})
export class MyApp {
  rootPage = HomePage;

  constructor(platform: Platform) {
    platform.ready().then(() =&gt; {


      var config = {
        apiKey: ".....",
        authDomain: "......",
        databaseURL: ".....",
        storageBucket: ".....",
        messagingSenderId: "......"
      };

      firebase.initializeApp(config);
      StatusBar.styleDefault();
    });
  }
}
</code></pre>

<p><strong>app.module.ts</strong></p>

<pre><code>import { NgModule } from '@angular/core';
import { IonicApp, IonicModule } from 'ionic-angular';
import { MyApp } from './app.component';
import { HomePage } from '../pages/home/home';

@NgModule({
  declarations: [
    MyApp,
    HomePage
  ],
  imports: [
    IonicModule.forRoot(MyApp)
  ],
  bootstrap: [IonicApp],
  entryComponents: [
    MyApp,
    HomePage 
  ],
  providers: []
})
export class AppModule {}
</code></pre>

<p><strong>My system information:</strong></p>

<p>Cordova CLI: 6.3.1</p>

<p>Ionic Framework Version: 2.0.0-rc.1</p>

<p>Ionic CLI Version: 2.1.1</p>

<p>Ionic App Lib Version: 2.1.1</p>

<p>Ionic App Scripts Version: 0.0.36</p>

<p>OS: Distributor ID: Ubuntu Description: Ubuntu 16.04.1 LTS </p>

<p>Node Version: v4.2.6</p>