title: What is the @ symbol meaning in require?
body: <p>Recently I've seen many <code>require('@XXX')</code>, like</p>
  
  <pre><code>const PubSub = require(`@google-cloud/pubsub`);
  </code></pre>
  
  <p>what is this <code>@</code> meaning? where can I find the syntax?</p>