As per my understanding,
Portal pages are not single page applications (SPAs).
- You need build your dist using any js framework.
- Then place index.html in www/<portal_page>.
- Put js and css files in public/js and public/css folders
- Link assets in index.html
<script src="/assets/ABC/js/global.js"></script>
Here is a previous discussion on how to make portal page single page app