libjavascriptcoregtk-4.1-dev 2.40.2-1ubuntu2 (amd64 binary) in ubuntu mantic

 JavaScriptCore is the JavaScript engine used in WebKit. It consists
 of the following building blocks: lexer, parser, start-up interpreter
 (LLInt), baseline JIT, a low-latency optimizing JIT (DFG), and a
 high-throughput optimizing JIT (FTL).
 .
 This build comes from the GTK port of WebKit (API version 4.1).
 .
 This package contains the development files.