Native dropdowns have much (much!) better UX and accessibility than most custom dropdowns built with JavaScript. Same goes for native form validation. And there are many more examples. Using JavaScript does not necessarily improve UX.

Use the platform where it makes sense. Extend it with JavaScript where needed. Make it work for everybody and make it better for capable browsers. That is called progressive enhancement. OP did not say that you may never use JavaScript. Just be mindful about it when you do.