index.html

<html>
  <head>
    <meta charset="UTF-8">
    <title>Browser-connected REPL</title>
  </head>
  <body>
    <div id="content">
      <script type="text/javascript" src="javascript/main.js"></script>
      <script type="text/javascript" src="javascript/foo.js"></script>
      <script type="text/javascript">
        goog.require('foo');
      </script>
    </div>
  </body>
</html>