There's been a few flash runtimes in javascript and other languages. Most of them have been long abandoned.

https://github.com/tobeytailor/gordon

https://www.gnu.org/software/gnash/

In development:

https://github.com/lightspark/lightspark

https://github.com/ruffle-rs/ruffle

And then the most recent one, CheerpX, which as I understand it runs the Adobe flash runtime itself via wasm: https://leaningtech.com/pages/cheerpxflash.html

Which brings me to Java. Java left the browser even before flash did. Not all of these are javascript jvms, but all of them are intended to run Java applications in the browser (some are transpilers, others require code changes):

https://leaningtech.com/pages/cheerpj.html

https://github.com/java2script/java2script (this links to some less-complete projects)

https://github.com/Jivings/jsJVM

https://github.com/nurv/BicaVM

https://github.com/st-js/st-js/

https://github.com/plasma-umass/doppio

https://github.com/jtulach/bck2brwsr

https://www.keithschwarz.com/+script/

https://github.com/robterrell/orto

https://github.com/jdstroy/JavaPoly

https://gitlab.com/neoexpert/jvm/-/blob/master/jsjvm/README....

Wow, cheerpx looks promising. Thanks for sharing!

Java in the browser reminds of classic RuneScape and my favorite old game site Javagameplay. Great times