You just use the js primitives.
I'm looking more at things like the Django template library, handlebars, Go HTML templates, etc. etc. And most especially things written with the idea that code shouldn't be in templates. Template languages that were always capable of running code, and were simply separate languages so designers don't have to learn a general-purpose programming language but can learn just this focused thing they need are obviously not what I mean.
I've drunk from the "templates shouldn't have logic in them" well too, but I think as you scale up it just becomes impractical. And in that case, you're better off with a template that always knew it was going to have code in rather than a template language that was designed from the beginning to not have it, but had code sneak in through the back door anyhow. The first one will at least be designed. The second one... well....