In the Pseudoscripting with <noscript> article, James McKee explains a nice trick for writing CSS that detects when Javascript is disabled.
It combines the <noscript> element with a Container Style Query, to provide clearly defined CSS classes that are active/inactive whenever Javascript is enabled/disabled.

I took this as inspiration to make some recently added Javascript-only pages on the blog degrade a bit more gracefully for non-Javascript users.
In the case of the On this day page and the Search page, there is now a message shown explaining that this functionality requires Javascript.
This is done simply with the <noscript> element and works well.

Additionally I used a trick similar to the one from the article to hide the Javascript-only content with CSS on these pages (eg. the search form).
This is achieved with the following CSS class definition which hides elements when Javascript is not enabled.

<noscript>
  <style>
    .js-only { display: none !important; }
  </style>
</noscript>

With this in place, I can now mark all Javascript-only elements with the js-only class.
They are then hidden when someone uses the page with Javascript disabled, and visible for everyone else.