libjavascriptcoregtk-4.0-dev 2.36.3-0ubuntu0.20.04.1 (s390x binary) in ubuntu focal

 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 4.0).
 .
 This package contains the development files.