It's actually fairly easy to get most of a Smalltalk out of Javascript. Prototypes and first-class functions form a really powerful basis for a higher language. Though, to your point, it wouldn't really still be Javascript.
Mootools: ancient class system for Javascript. https://mootools.net/core
Also, here's a very old Crockford article on implementing classes in Javascript. https://crockford.com/javascript/inheritance.html