diff --git a/.babelrc.json b/.babelrc.json
index 11b4177..245463a 100644
--- a/.babelrc.json
+++ b/.babelrc.json
@@ -13,8 +13,7 @@
       ],
       "env": {
         "cjs": {
-          "presets": [["@babel/preset-env", { "modules": "commonjs" }]],
-          "plugins": ["./resources/inline-invariant"]
+          "presets": [["@babel/preset-env", { "modules": "commonjs" }]]
         },
         "mjs": {
           "presets": [["@babel/preset-env", { "modules": false }]],
diff --git a/.eslintignore b/.eslintignore
index cde39e0..5002fc1 100644
--- a/.eslintignore
+++ b/.eslintignore
@@ -1,4 +1,4 @@
 # Copied from '.gitignore', please keep it in sync.
 node_modules
 coverage
-lib
+dist
diff --git a/.eslintrc.yml b/.eslintrc.yml
index 6be0b2a..9845199 100644
--- a/.eslintrc.yml
+++ b/.eslintrc.yml
@@ -478,4 +478,21 @@ overrides:
       no-console: off
   - files: '**/__*__/**'
     rules:
+      node/no-unpublished-import: off
       import/no-extraneous-dependencies: [error, { devDependencies: true }]
+  - files: 'resources/**'
+    parserOptions:
+      sourceType: script
+    rules:
+      node/no-unpublished-import: off
+      node/no-unpublished-require: off
+      node/no-missing-require: off
+      node/no-sync: off
+      node/no-unsupported-features/node-builtins: off
+      node/global-require: off
+      import/no-dynamic-require: off
+      import/no-extraneous-dependencies: [error, { devDependencies: true }]
+      import/no-nodejs-modules: off
+      import/no-commonjs: off
+      no-await-in-loop: off
+      no-console: off
diff --git a/.gitignore b/.gitignore
index 38c8972..6fb641c 100644
--- a/.gitignore
+++ b/.gitignore
@@ -7,4 +7,4 @@
 
 node_modules
 coverage
-lib
+dist
diff --git a/.prettierignore b/.prettierignore
index cde39e0..5002fc1 100644
--- a/.prettierignore
+++ b/.prettierignore
@@ -1,4 +1,4 @@
 # Copied from '.gitignore', please keep it in sync.
 node_modules
 coverage
-lib
+dist
diff --git a/package.json b/package.json
index 83fe546..7aae733 100644
--- a/package.json
+++ b/package.json
@@ -11,15 +11,7 @@
     "type": "git",
     "url": "http://github.com/graphql/graphql-relay-js.git"
   },
-  "main": "lib/index.js",
-  "directories": {
-    "lib": "./lib"
-  },
-  "files": [
-    "lib",
-    "README.md",
-    "LICENSE"
-  ],
+  "main": "index.js",
   "scripts": {
     "prepublish": "./resources/prepublish.sh",
     "prettier": "prettier --write --list-different .",
@@ -29,8 +21,7 @@
     "testonly:cover": "nyc npm run testonly",
     "lint": "eslint .",
     "check": "flow check",
-    "build": "rm -rf lib/* && babel src --ignore __tests__ --out-dir lib && npm run build:flow",
-    "build:flow": "find ./src -name '*.js' -not -path '*/__tests__*' | while read filepath; do cp $filepath `echo $filepath | sed 's/\\/src\\//\\/lib\\//g'`.flow; done"
+    "build": "node resources/build.js"
   },
   "peerDependencies": {
     "graphql": "^14.0.0 || ^15.0.0"
diff --git a/resources/build.js b/resources/build.js
new file mode 100644
index 0000000..4310e64
--- /dev/null
+++ b/resources/build.js
@@ -0,0 +1,116 @@
+// @noflow
+
+'use strict';
+
+const fs = require('fs');
+const path = require('path');
+const assert = require('assert');
+
+const babel = require('@babel/core');
+
+const { rmdirRecursive, readdirRecursive } = require('./utils');
+
+if (require.main === module) {
+  rmdirRecursive('./dist');
+  fs.mkdirSync('./dist');
+
+  const srcFiles = readdirRecursive('./src', { ignoreDir: /^__.*__$/ });
+  for (const filepath of srcFiles) {
+    const srcPath = path.join('./src', filepath);
+    const destPath = path.join('./dist', filepath);
+
+    fs.mkdirSync(path.dirname(destPath), { recursive: true });
+    if (filepath.endsWith('.js')) {
+      fs.copyFileSync(srcPath, destPath + '.flow');
+
+      const cjs = babelBuild(srcPath, { envName: 'cjs' });
+      fs.writeFileSync(destPath, cjs);
+    } else if (filepath.endsWith('d.ts')) {
+      fs.copyFileSync(srcPath, destPath);
+    }
+  }
+
+  fs.copyFileSync('./LICENSE', './dist/LICENSE');
+  fs.copyFileSync('./README.md', './dist/README.md');
+
+  // Should be done as the last step so only valid packages can be published
+  const packageJSON = buildPackageJSON();
+  fs.writeFileSync('./dist/package.json', JSON.stringify(packageJSON, null, 2));
+
+  showStats();
+}
+
+function babelBuild(srcPath, options) {
+  return babel.transformFileSync(srcPath, options).code + '\n';
+}
+
+function buildPackageJSON() {
+  const packageJSON = require('../package.json');
+  delete packageJSON.private;
+  delete packageJSON.scripts;
+  delete packageJSON.devDependencies;
+
+  const { version } = packageJSON;
+  const versionMatch = /^\d+\.\d+\.\d+-?(.*)?$/.exec(version);
+  if (!versionMatch) {
+    throw new Error('Version does not match semver spec: ' + version);
+  }
+
+  const [, preReleaseTag] = versionMatch;
+
+  if (preReleaseTag != null) {
+    const [tag] = preReleaseTag.split('.');
+    assert(['alpha', 'beta', 'rc'].includes(tag), `"${tag}" tag is supported.`);
+
+    assert(!packageJSON.publishConfig, 'Can not override "publishConfig".');
+    packageJSON.publishConfig = { tag: tag || 'latest' };
+  }
+
+  return packageJSON;
+}
+
+function showStats() {
+  const fileTypes = {};
+  let totalSize = 0;
+
+  for (const filepath of readdirRecursive('./dist')) {
+    const name = filepath.split(path.sep).pop();
+    const [base, ...splitExt] = name.split('.');
+    const ext = splitExt.join('.');
+
+    const filetype = ext ? '*.' + ext : base;
+    fileTypes[filetype] = fileTypes[filetype] || { filepaths: [], size: 0 };
+
+    const { size } = fs.lstatSync(path.join('./dist', filepath));
+    totalSize += size;
+    fileTypes[filetype].size += size;
+    fileTypes[filetype].filepaths.push(filepath);
+  }
+
+  let stats = [];
+  for (const [filetype, typeStats] of Object.entries(fileTypes)) {
+    const numFiles = typeStats.filepaths.length;
+
+    if (numFiles > 1) {
+      stats.push([filetype + ' x' + numFiles, typeStats.size]);
+    } else {
+      stats.push([typeStats.filepaths[0], typeStats.size]);
+    }
+  }
+  stats.sort((a, b) => b[1] - a[1]);
+  stats = stats.map(([type, size]) => [type, (size / 1024).toFixed(2) + ' KB']);
+
+  const typeMaxLength = Math.max(...stats.map((x) => x[0].length));
+  const sizeMaxLength = Math.max(...stats.map((x) => x[1].length));
+  for (const [type, size] of stats) {
+    console.log(
+      type.padStart(typeMaxLength) + ' | ' + size.padStart(sizeMaxLength),
+    );
+  }
+
+  console.log('-'.repeat(typeMaxLength + 3 + sizeMaxLength));
+  const totalMB = (totalSize / 1024 / 1024).toFixed(2) + ' MB';
+  console.log(
+    'Total'.padStart(typeMaxLength) + ' | ' + totalMB.padStart(sizeMaxLength),
+  );
+}
diff --git a/resources/utils.js b/resources/utils.js
new file mode 100644
index 0000000..82be6b3
--- /dev/null
+++ b/resources/utils.js
@@ -0,0 +1,46 @@
+// @noflow
+
+'use strict';
+
+const fs = require('fs');
+const path = require('path');
+
+function rmdirRecursive(dirPath) {
+  if (fs.existsSync(dirPath)) {
+    for (const dirent of fs.readdirSync(dirPath, { withFileTypes: true })) {
+      const fullPath = path.join(dirPath, dirent.name);
+      if (dirent.isDirectory()) {
+        rmdirRecursive(fullPath);
+      } else {
+        fs.unlinkSync(fullPath);
+      }
+    }
+    fs.rmdirSync(dirPath);
+  }
+}
+
+function readdirRecursive(dirPath, opts = {}) {
+  const { ignoreDir } = opts;
+  const result = [];
+  for (const dirent of fs.readdirSync(dirPath, { withFileTypes: true })) {
+    const name = dirent.name;
+    if (!dirent.isDirectory()) {
+      result.push(dirent.name);
+      continue;
+    }
+
+    if (ignoreDir && ignoreDir.test(name)) {
+      continue;
+    }
+    const list = readdirRecursive(path.join(dirPath, name), opts).map((f) =>
+      path.join(name, f),
+    );
+    result.push(...list);
+  }
+  return result;
+}
+
+module.exports = {
+  rmdirRecursive,
+  readdirRecursive,
+};