src/404.html

<!DOCTYPE html>
<html>
  <head>
    <meta charset="utf-8" />
    <title>Single Page Apps for GitHub Pages</title>
    <script type="text/javascript">
      /**
       * Single Page Apps for GitHub Pages
       *
       * Ref: https://github.com/rafrex/spa-github-pages
       * Copyright (c) 2016 Rafael Pedicini, licensed under the MIT License
       *
       * This script takes the current URL, converts the path and query
       * string into just a query string, and then redirects the browser
       * to the new URL with only a query string and hash fragment.
       *
       * For example:
       *   http://www.foo.tld/one/two?a=b&c=d#qwe
       *   [BECOMES]
       *   http://www.foo.tld/?/one/two&q=a=b~and~c=d#qwe
       *
       * Note: This 404.html file must be at least 512 bytes for it to work
       * with Internet Explorer (it is currently > 512 bytes).
       *
       * Note: If you are setting up a GitHub Pages site and not using a
       * custom domain (i.e. your site's address is username.github.io/repo-name),
       * then you need to set `pathSegmentsToKeep` to 1 in order to keep `/repo-name`
       * in the path after the redirect. Otherwise, leave pathSegmentsToKeep as 0.
       *
       * For example:
       *   https://username.github.io/repo-name/one/two?a=b&c=d#qwe
       *   [BECOMES]
       *   https://username.github.io/repo-name/?/one/two&q=a=b~and~c=d#qwe
       */
      let pathSegmentsToKeep = 0;
      let l = window.location;
      l.replace(
        l.protocol +
          "//" +
          l.hostname +
          (l.port ? ":" + l.port : "") +
          l.pathname
            .split("/")
            .slice(0, 1 + pathSegmentsToKeep)
            .join("/") +
          "/?/" +
          l.pathname
            .slice(1)
            .split("/")
            .slice(pathSegmentsToKeep)
            .join("/")
            .replace(/&/g, "~and~") +
          (l.search ? "&" + l.search.slice(1).replace(/&/g, "~and~") : "") +
          l.hash
      );
    </script>
  </head>
  <body></body>
</html>