Many projects still provide instructions for how to make use of a JS library from a CDN or local file but many do not. Many just assume you’ve got npm or yarn or similar.
I have ambivalent feelings about this. Notepad and a browser might have been all you needed in the past, but it was never really all that great. There are a lot of benefits to having a build step: linters; alternate languages like typescript, markup, scss, and haml; script minimization; image resizing; and so on.
Recently I found the browser’s dev tools stopped printing warnings for unknown CSS properties, so the old notepad-and-browser approach won’t even catch typos like it used to. That makes a linter even more essential.