Write JavaScript functions - use as bash functions

jsfunc.sh

#!/bin/bash
jsfunc() {
  local code="$(cat)"
  local fn="$(cat <<EOFF
$1() {
  node <(cat <<EOF
require('stream').Readable.prototype.then = function (...args) { return new Promise((res, rej) => { const bufs = []; this.on('error', rej).on('data', buf => bufs.push(buf)).on('end', () => res(Buffer.concat(bufs))); }).then(...args) };
(async () => {
${code}
})().then(val => typeof val !== 'undefined' && console.log(typeof val === 'string' ? val : JSON.stringify(val, null, 2))).catch(err => console.error(err.stack) || process.exit(1));
EOF
) "\$@"
}
EOFF
)"
  eval "${fn}"
}

usage.sh

#!/bin/bash
source ./jsfunc.sh

jsfunc my_js_func <<EOF
  const stdin = String(await process.stdin);
  return (stdin + ' ' + process.argv[2]).toUpperCase();
EOF

printf hello | my_js_func world
# HELLO WORLD