libjs-of-ocaml-dev binary package in Ubuntu Focal s390x

 Js_of_ocaml is a compiler of OCaml bytecode to JavaScript. It makes
 it possible to run OCaml programs in a web browser. Its key features
 are the following:
  * the whole language, and most of the standard library are
    supported;
  * the generated code can be used with any web server and browser;
  * you can use a standard installation of OCaml to compile your
    programs. In particular, you do not have to recompile a library to
    use it with Js_of_ocaml. You just have to link your program with a
    specific library to interface with the browser APIs.
 .
 This package contains development files needed to compile server-side
 (using regular OCaml compiler) and client-side (using Js_of_ocaml)
 programs.

Source package