"there aren't good tools for automated testing without a build step" For our vanilla JS we use browser-based tests which we can check in any browser anywhere a

"there aren't good tools for automated testing without a build step" For our vanilla JS we use browser-based tests which we can check in any browser anywhere any time, and which can also be automated and measured with a headless browser from the command line. And we have also used Node and had even more luck with Deno for testing individual functions and libraries which may get used on the frontend! Hope that helps!