What is this code in the Firebase CLI-generated index.html file?

Question

I used the firebase CLI to deploy a site. The tool generated the index.html file. At the bottom of it was the following script. Can anyone tell me what it is supposed to be for, and why are some parts commented out?

<script>
  document.addEventListener('DOMContentLoaded', function() {
    // // 🔥🔥🔥🔥🔥🔥🔥🔥🔥🔥🔥🔥🔥🔥🔥🔥🔥🔥🔥🔥🔥🔥🔥🔥🔥🔥🔥🔥🔥🔥🔥
    // // The Firebase SDK is initialized and available here!
    //
    // firebase.auth().onAuthStateChanged(user => { });
    // firebase.database().ref('/path/to/ref').on('value', snapshot => { });
    // firebase.messaging().requestPermission().then(() => { });
    // firebase.storage().ref('/path/to/ref').getDownloadURL().then(() => { });
    //
    // // 🔥🔥🔥🔥🔥🔥🔥🔥🔥🔥🔥🔥🔥🔥🔥🔥🔥🔥🔥🔥🔥🔥🔥🔥🔥🔥🔥🔥🔥🔥🔥

    try {
      let app = firebase.app();
      let features = ['auth', 'database', 'messaging', 'storage'].filter(feature => typeof app[feature] === 'function');
      document.getElementById('load').innerHTML = `Firebase SDK loaded with ${features.join(', ')}`;
    } catch (e) {
      console.error(e);
      document.getElementById('load').innerHTML = 'Error loading the Firebase SDK, check the console.';
    }
  });
</script>

Answer 1

The commented-out parts are just brief samples you can copy to work with the various parts of the Firebase SDK for JavaScript. You can take them or leave them.

The uncommented code will print out on the web page which Firebase products you're currently using in that page. You should remove it when you're done with it. It doesn't do anything important.