I am creating an HTML template can I use JavaScript for this template. I can not understand this line also Ensure your item does not require Javascript to function. This category is exclusively for high-level CSS components which go above and beyond what is readily available for free on the web.
where have you found the line?
https://help.author.envato.com/hc/en-us/articles/360000471583-Code-Item-Preparation-Technical-Requirements#h_01F14H85RRYS8D5AB3V4D5YW4Y I found this from above link
That one for HTML5 category in CodeCanyon.
For HTML site template you are free to use JS assets.