index.html

<!DOCTYPE html>
<html>
  <head>
    <meta charset="UTF-8">
    <link href="assets/material-icons.css" rel="stylesheet">
    <link href="index.css" rel="stylesheet">
    <title>Tau</title>
  </head>
  <body>
    <div id="app"></div>
    <script>
      const { remote } = require("electron");
      let bundlePath = './bundle/renderer.bundle.js';
      if (remote.process.env.NODE_ENV === 'DEV') {
        const port = process.env.PORT || 8080;
        bundlePath = `http://localhost:${port}/bundle/renderer.bundle.js`;
        const bundleScriptEl = document.createElement('script');
        bundleScriptEl.src = bundlePath;
        bundleScriptEl.async = true;
        document.currentScript.parentNode.insertBefore(bundleScriptEl, document.currentScript);
      } else {
        require(bundlePath);
      }
    </script>
  </body>
</html>