<!DOCTYPE html>
<html>
  <head>
    <meta charset="utf-8">
    <title>Hello</title>
    <link rel="stylesheet" href="/css/main.css" media="screen" charset="utf-8">
    <script src="/js/bundle.js" charset="utf-8"></script>
  </head>
  <body>
    <header>
      <h1>Class 3-10 (2016)</h1>
    </header>
    <div class="button">
      <a href="/pdf">Print</a>
    </div>
    <div class="wrapper"></div>
  </body>
</html>

<!DOCTYPE html>
<html>
  <head>
    <meta charset="utf-8">
    <title>Hello</title>
    <link rel="stylesheet" href="/css/main.css" media="screen" charset="utf-8">
    <script defer src="/js/out.js" charset="utf-8"></script>
  </head>
  <body>
    <header>
      <h1>Class 3-10 (2016)</h1>
    </header>
    <div class="button">
      <a href="/pdf">Print</a>
    </div>
    <div class="wrapper"></div>
  </body>
</html>

Add defer to script tag
Add defer to script tag
