postbuild.js

const fs = require('fs');
const archiver = require('archiver');

fs.unlinkSync('./docs/app.bundle.js');

let output = fs.createWriteStream('./game.zip');
let archive = archiver('zip', {
  zlib: { level: 9 } // set compression to best
});

const MAX = 13 * 1024; // 13kb

output.on('close', function () {
  const bytes = archive.pointer();
  const percent = (bytes / MAX * 100).toFixed(2);
  if (bytes > MAX) {
    console.error(`Size overflow: ${bytes} bytes (${percent}%)`)
  } else {
    console.log(`Size: ${bytes} bytes (${percent}%)`)
  }
});

archive.on('warning', function (err) {
  if (err.code === 'ENOENT') {
    console.warn(err)
  } else {
    throw err
  }
});

archive.on('error', function (err) {
  throw err
});

archive.pipe(output);
archive.append(
  fs.createReadStream('./docs/index.html'), {
    name: 'index.html'
  }
);

archive.finalize();