title: Angular 6 Show progress of app bootstrapping
body: <p>I have a small project that has packages (<code>angular cdk</code>, <code>angular material</code>, and <code>firebase</code>). Yet I have a built <code>vendor.js</code> file with size <code>4 MB</code>. </p>
  
  <p>As an approach to deal with problem, I want to show the progress of loading on slow connections (it takes up to 2 minutes to load 4 MB), so that users can see app is loading. </p>
  
  <p>I have installed <code>PWA</code> and <code>service-worker</code> so that the app does not reload each time.</p>