chore: add a script to compute the bundle size

package.json

@@ -98,6 +98,7 @@
     "test:node-fetch": "USE_FETCH=1 npm run test:node",
     "test:browser": "zuul test/index.js",
     "build": "rollup -c support/rollup.config.umd.js && rollup -c support/rollup.config.esm.js",
+    "bundle-size": "node support/bundle-size.js",
     "format:check": "prettier --check 'lib/**/*.ts' 'test/**/*.js' 'test/webtransport.mjs' 'support/**/*.js'",
     "format:fix": "prettier --write 'lib/**/*.ts' 'test/**/*.js' 'test/webtransport.mjs' 'support/**/*.js'",
     "prepack": "npm run compile"

support/bundle-size.js

@@ -0,0 +1,35 @@
+const { resolve } = require("node:path");
+const { readFile } = require("node:fs/promises");
+const { gzipSync, brotliCompressSync } = require("node:zlib");
+
+const bundles = [
+  {
+    name: "UMD bundle",
+    path: "dist/engine.io.min.js",
+  },
+  {
+    name: "ESM bundle",
+    path: "dist/engine.io.esm.min.js",
+  },
+];
+
+function format(size) {
+  return (size / 1024).toFixed(1);
+}
+
+async function main() {
+  for (const bundle of bundles) {
+    const path = resolve(bundle.path);
+    const content = await readFile(path);
+    const gzip = gzipSync(content);
+    const brotli = brotliCompressSync(content);
+
+    console.log(`${bundle.name}`);
+    console.log(`min: ${format(content.length)} KB`);
+    console.log(`min+gzip: ${format(gzip.length)} KB`);
+    console.log(`min+br: ${format(brotli.length)} KB`);
+    console.log();
+  }
+}
+
+main();