computeBrotliSize.mjs

#!/usr/bin/env node

import { promises as fs, createReadStream } from "fs";
import { createBrotliCompress } from "zlib";
import { resolve, join } from "path";

const DIR = resolve(process.argv[2]);

fs.readdir(DIR)
  .then(files =>
    Promise.all(
      files.map(
        fileName =>
          new Promise(async (resolve, reject) => {
            const filePath = join(DIR, fileName);
            const stats = await fs.stat(filePath);
            if (stats.isFile()) {
              const stream = createReadStream(filePath).pipe(
                createBrotliCompress()
              );
              let counter = 0;
              stream.once("error", reject);
              stream.on("data", chunk => {
                counter += chunk.length;
              });
              stream.on("end", () =>
                resolve([
                  fileName,
                  {
                    uncompressedSize: stats.size,
                    brotliSize: counter,
                    ratio: counter / stats.size,
                  },
                ])
              );
            } else {
              resolve([fileName, null]);
            }
          })
      )
    )
  )
  .then(Object.fromEntries)
  .then(console.log)
  .catch(console.error);