How to compile ffish.js into a version that can be converted by browserify?

[yjf2002ghty]

I'm trying to test my recent pull requests by putting the results into Fairyground and have some further runs.
However, when I compiled ffish.js, browserify is unable to make the conversion to CommonJS which makes it runnable in a browser. None of the following commands worked:
make -f Makefile_js build
make -f Makefile_js build es6=yes

Browserify keeps showing the following error:

SyntaxError: Unexpected token (716:26) while parsing E:\Chess\new\fairyground-main\node_modules\ffish-es6\ffish.js while parsing file: E:\Chess\new\fairyground-main\node_modules\ffish-es6\ffish.js
    at DestroyableTransform.end [as _flush] (E:\Chess\new\fairyground-main\node_modules\insert-module-globals\index.js:114:21)
    at DestroyableTransform.prefinish (E:\Chess\new\fairyground-main\node_modules\readable-stream\lib\_stream_transform.js:138:10)
    at DestroyableTransform.emit (node:events:513:28)
    at prefinish (E:\Chess\new\fairyground-main\node_modules\readable-stream\lib\_stream_writable.js:619:14)
    at finishMaybe (E:\Chess\new\fairyground-main\node_modules\readable-stream\lib\_stream_writable.js:627:5)
    at endWritable (E:\Chess\new\fairyground-main\node_modules\readable-stream\lib\_stream_writable.js:638:3)
    at Writable.end (E:\Chess\new\fairyground-main\node_modules\readable-stream\lib\_stream_writable.js:594:41)
    at DuplexWrapper.onend (E:\Chess\new\fairyground-main\node_modules\readable-stream\lib\_stream_readable.js:577:10)
    at Object.onceWrapper (node:events:627:28)
    at DuplexWrapper.emit (node:events:525:35)

I've also checked the difference between the compiled file and the file comes from NPM package. It seems that the compiled version from Makefile adds a lot of __syscall objects while the distributed one does not.

How to compile ffish.js into a version that can be converted by browserify?