hyperscript is a separate project. It is not a feature of htmx. htmx handles the hypermedia interactions with the back-end server. For pure in-page interactivity (hiding/showing side-navs, etc), you get to decide how you want to do it: VanillaJS, AlpineJS (my favourite), hyperscript, Web Components (lit.dev, etc), StimulusJS (what you used), a big framework component (Svelte, Vue, React, ...), etc, etc. htmx does not bundle anything into itself to make that decision for you. You may have thought hyperscript is a feature of htmx because sometimes you'll see the two used in examples (both have the same creator).