title: "unreachable code after return statement" error in Google Analytics JS code on Firefox - is this my fault?
body: <p>I'm using the current Google Analytics tracking code, and on Firefox 59 I get this error in console: </p>
  
  <blockquote>
    <p>unreachable code after return statement</p>
  </blockquote>
  
  <p>On this javascript: <a href="https://www.googletagmanager.com/gtag/js?id=UA-my-tracking-code:formatted" rel="noreferrer">https://www.googletagmanager.com/gtag/js?id=UA-my-tracking-code:formatted</a></p>
  
  <p>Since this problem doesn't seem to be googleable, hence it seems others do not have this problem, my guess is that it's me who does something wrong. But what this could be?</p>
  
  <p>I'm putting the snippet in <code>&lt;head&gt;</code>, just like the docs say:</p>
  
  <pre><code>&lt;!DOCTYPE html&gt;
  &lt;html&gt;
      &lt;head&gt;
          &lt;title&gt;some title&lt;/title&gt;
          &lt;meta charset="UTF-8"&gt;
          &lt;meta name="viewport" content="width=device-width, initial-scale=1.0"&gt;
  
          &lt;!-- Global site tag (gtag.js) - Google Analytics --&gt;
          &lt;script async src="https://www.googletagmanager.com/gtag/js?id=UA-my-tracking-code"&gt;&lt;/script&gt;
  
          &lt;script&gt;
            window.dataLayer = window.dataLayer || [];
            function gtag(){dataLayer.push(arguments);}
            gtag('js', new Date());
            gtag('config', 'UA-my-tracking-code');
          &lt;/script&gt;
  
      &lt;/head&gt;
      &lt;body&gt;
       blah blah 
      &lt;/body&gt;
  &lt;/html&gt;
  </code></pre>