Hack for using Scala.js + ES modules + Google Closure Compiler

externs.js

var require;

// scala.js externs

    //var Object;
    Object.prototype.constructor;
    Object.prototype.toString;
    Object.prototype.$classData;
    //var Array;
    Array.prototype.length;
    //var Function;
    Function.prototype.call;
    Function.prototype.apply;
    //var NaN = 0.0/0.0; //, /*Infinity = 1.0/0.0,*/ undefined = void 0;

optimize.sh

#!/bin/bash
# safety settings
set -u
set -e
set -o pipefail

DIR="$(dirname -- "$(realpath -- "$0")")"
echo $DIR

cd "$DIR"/zbdb-stats/client/target/scala-3.3.1/zbdb-stats-client-opt

## Idenpotent in-place fixes
# Current Closure Compiler doesn't like the escape sequence, so fix it
sed -i 's/_\\uff3fself/_xxuff3fselfg/' internal-*.js
# Replace imports with requires for external libraries
sed -i 's#import \* as \([^ ]\+\) from \("[^.].*"\);#const \1 = require(\2);#' internal-*.js
# Create a launcher script
echo 'import * as App from "./client.js";
App.main(null);
' > client.run.js

## Compilation
npx google-closure-compiler@v20220202 \
	-O ADVANCED \
	--externs "$DIR"/externs.js \
	--language_in=ES_NEXT \
	--module_resolution=NODE \
	client.run.js client.js internal-*.js \
	--entry_point=client.run.js \
	> opt.js

## Postprocessing
# Replace requires by imports except the last one
lasthash=""
while [ "$lasthash" != "$(sha256sum opt.js)" ]; do
	lasthash="$(sha256sum opt.js)"
	sed -i 's/const \([^=]\+\)=require(\("[^"]\+"\)),/import * as \1 from \2; const /' opt.js
done
# Replace the last one
lasthash=""
while [ "$lasthash" != "$(sha256sum opt.js)" ]; do
	lasthash="$(sha256sum opt.js)"
	sed -i 's/const \([^=]\+\)=require(\("[^"]\+"\));/import * as \1 from \2;/' opt.js
done

## Show the output stats
wc -c opt.js
ls -lh opt.js