main.js

import { writeFile } from 'node:fs/promises';

let ctors;
let rev;
let combine;
let save2file;
let message;

message = 'Hello from More !';

save2file = async (msg, filename) => {
    const buf = mkos(msg);
    await writeFile(filename, buf, { encoding: 'binary' });
    return true;
};

combine = (a, b) =>
    ((a & 0xff) << 8)
    | (b & 0xff);

rev = val => {
    const a = val & 0xff;
    const b = (val & 0xff00) >> 8;
    return String.fromCharCode(a) + String.fromCharCode(b);
};

ctors = {
    copy2ax: val => "\xb8" + rev(val),
    copy2bx: val => "\xbb" + rev(val),
    copy2cx: val => "\xb9" + rev(val),
    copy2sp: () => "\x89\xc4",
    biosinterrupt: () => "\xcd\x10",
    interruptoff: () => "\xfa",
    halt: () => "\x90\xf4",
    jmp: () => "\xeb\xfc",
    padding: amt => "\x90".repeat(amt),
    magic: () => rev(0xaa55),
    print: str => str
        .concat('\r\n')
        .split('')
        .map(x => ctors.copy2ax(combine(0x0e, x.charCodeAt(0)))
            .concat(ctors.biosinterrupt()))
        .join('')
};

let mkos;
let part1;
let part2;
let exitval;
let file;

mkos = msg =>
    part1(msg)
    + part2(510 - part1(msg).length);

part1 = msg =>
    ctors.copy2ax(0xfbff)
    + ctors.copy2sp()
    + ctors.copy2bx(0x0000)
    + ctors.print(msg)
    + ctors.halt()
    + ctors.jmp();

part2 = amt =>
    ctors.padding(amt)
    + ctors.magic();

file = process.argv[2];
if (!file) {
    console.error('Usage: ' + process.argv[1], '<filename>');
    process.exit(1);
}

exitval = await save2file(message, file);
if (exitval)
    console.log('ok');
else
    console.error('failed');