feat: add --preserve-modules flag for tree-shaking support

Author: carlostxm

CHANGELOG.md

@@ -7,6 +7,12 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ## [Unreleased]
 
+## [0.2.0] - 2025-12-15
+
+### Added
+
+- New `--preserve-modules` (or `-m`) flag to enable tree-shaking optimization. When enabled, Rollup generates individual files preserving the source directory structure instead of a single monolithic bundle. This allows consumers using modern bundlers to effectively tree-shake unused exports, significantly reducing bundle sizes for libraries with many exports (e.g., icon libraries).
+
 ## [0.1.2] - 2022-06-05
 
 ### Fixed

README.md

@@ -23,6 +23,36 @@ NOTICE: this package doesn't clean your build directories in each run, so you'd
 
 - `-w` to watch the files.
 - `-p` to define a different `tsconfig.ts` file. p.eg: `package-build -p tsconfig.build.json`.
+- `-m` or `--preserve-modules` to enable tree-shaking optimization (see below).
+
+#### Tree Shaking Optimization
+
+For libraries with many exports (like icon libraries), use the `--preserve-modules` flag to generate individual files instead of a single bundle:
+
+```bash
+package-build --preserve-modules
+package-build -m
+```
+
+This enables effective tree-shaking for consumers using modern bundlers. When enabled:
+
+- Output files are generated in `dist/` (CJS) and `es2015/` (ESM) directories
+- The source directory structure is preserved
+- Each module becomes a separate file instead of being bundled into one
+
+**Recommended package.json configuration for tree-shakable libraries:**
+
+```json
+{
+  "sideEffects": false,
+  "exports": {
+    ".": {
+      "import": "./es2015/index.js",
+      "require": "./dist/index.js"
+    }
+  }
+}
+```
 
 ### Publish a new version
 

build.js

@@ -33,10 +33,16 @@ const watch = (config) => {
   watcher.on('event', (event) => eventHandler(event));
 };
 
-const build = async (withWatch = false, project) => {
+const build = async (withWatch = false, project, options = {}) => {
   const dirname = process.cwd();
+  const { preserveModules = false } = options;
+
   console.log(`Bundling ${dirname}`);
-  const { input, output } = getRollupConfig(dirname, project);
+  if (preserveModules) {
+    console.log('Using preserveModules mode for tree-shaking optimization');
+  }
+
+  const { input, output } = getRollupConfig(dirname, project, options);
 
   if (withWatch) {
     watch({ ...input, output });
@@ -45,7 +51,8 @@ const build = async (withWatch = false, project) => {
       const bundle = await rollup.rollup(input);
       await Promise.all(
         output.map(async (outputItem) => {
-          console.log(`Bundling ${outputItem.format} into ${outputItem.file}`);
+          const target = outputItem.dir || outputItem.file;
+          console.log(`Bundling ${outputItem.format} into ${target}`);
           return bundle.write(outputItem);
         }),
       );
@@ -60,4 +67,8 @@ const build = async (withWatch = false, project) => {
 
 const argv = minimist(process.argv.slice(2));
 
-build(argv.w, argv.p);
+const options = {
+  preserveModules: argv.m || argv['preserve-modules'] || false,
+};
+
+build(argv.w, argv.p, options);

getRollupConfig.js

@@ -15,7 +15,8 @@ const compileTypings = (cwd) => () => {
   });
 };
 
-module.exports = (dirname, project) => {
+module.exports = (dirname, project, options = {}) => {
+  const { preserveModules = false } = options;
   const pkgPath = path.join(dirname, 'package.json');
   // eslint-disable-next-line import/no-dynamic-require, global-require
   const pkg = require(pkgPath);
@@ -27,6 +28,31 @@ module.exports = (dirname, project) => {
 
   const extensions = ['.js', '.jsx', '.ts', '.tsx'];
 
+  const getOutputConfig = (format) => {
+    const baseConfig = {
+      sourcemap: true,
+      interop: 'auto',
+    };
+
+    if (preserveModules) {
+      return {
+        ...baseConfig,
+        dir: format === 'cjs' ? 'dist' : 'es2015',
+        format,
+        preserveModules: true,
+        preserveModulesRoot: 'src',
+        entryFileNames: '[name].js',
+      };
+    }
+
+    // Legacy mode: single bundle file
+    return {
+      ...baseConfig,
+      file: format === 'cjs' ? pkg.main : pkg.module,
+      format,
+    };
+  };
+
   return {
     input: {
       input: `${dirname}/src/index.ts`,
@@ -60,19 +86,6 @@ module.exports = (dirname, project) => {
         }),
       ],
     },
-    output: [
-      {
-        file: pkg.main,
-        format: 'cjs',
-        sourcemap: true,
-        // See: https://rollupjs.org/configuration-options/#output-interop
-        interop: 'auto',
-      },
-      {
-        file: pkg.module,
-        format: 'esm',
-        sourcemap: true,
-      },
-    ],
+    output: [getOutputConfig('cjs'), getOutputConfig('esm')],
   };
 };

package.json

@@ -8,6 +8,9 @@
   "bin": {
     "package-build": "./bin/runner.js"
   },
+  "engines": {
+    "node": ">=20.0.0"
+  },
   "scripts": {
     "build": "echo 'No build script required.'",
     "test": "npm run lint:check && npm run format:check",
@@ -52,7 +55,7 @@
     "typescript": ">= 3.7"
   },
   "volta": {
-    "node": "18.16.0",
+    "node": "20.18.1",
     "yarn": "1.22.19"
   },
   "publishConfig": {