Test coverage of plain JS, preferably w/o npm?

I’m unit-testing some JS, with Jasmine, and I’d like to check our coverage. We’re not using any front-end framework, nor much JS, so no other need to install npm, nor much additional other JS infrastructure, so we’d prefer not to. I’ve been trying to find lightweight options, and not coming up with anything, other than very clumsy dev-tools built into different browsers (and we haven’t standardized on one, and have customers that use different ones). Any ideas, if not of specific tools then at least where to look?

Most of the rest of the project is in Ruby, so gems are an option, but it’s not Rails and we definitely don’t want to drag that in as well. (It’s in Sinatra, but we may be moving away from that too, to just plain Rack. I doubt we’d go any lower-level than that though!) The only possibly-suitable thing I’ve found there is jscover, which hasn’t been updated in forever and depends strictly on such an outdated version of v8 that it’s a PITA to install it (in fact I tried for about four hours yesterday with all kinds of workarounds and failed).

Other details: I’m on a Mac, but we need it to work on Linux for most of the rest of the team. Windows not needed. NONE of us are JS wizards, I’ve got a decent handle on the language basics and some basic DOM manipulation but that’s about it, and still seem to be in the lead. We can certainly cobble pieces together with Ruby, bash scripting, maybe a few other languages, and baling wire.