Most of my competitors (who provide client-side-only libs) were doing perpetual licensing, so I followed suit. However, there IS a recurring aspect: the customer gets email support and version upgrades for only a year. Then they must renew. It's opt-in, but I nudge them with email reminders.

I've seen a number of client-side-only products that ARE subscription (like Sencha), but they seem more general-purpose, like a framework. Something developers at a company would use everyday for everything. FullCalendar felt like more of a plug-n-play widget, not as pervasive.

Maybe your product is somewhere in between. It's pretty arbitrary nonetheless.