fix: Ensure CommonJS mode works correctly.

Rollup mangles dynamic imports and without a way to override that, I
instead switched the source code to CommonJS and then have it exported
from an ESM module for compatibility.

Fixes #6

package.json

@@ -2,16 +2,17 @@
   "name": "@humanwhocodes/module-importer",
   "version": "1.0.0",
   "description": "Universal module importer for Node.js",
-  "main": "dist/module-importer.cjs",
-  "module": "dist/module-importer.js",
+  "main": "src/module-importer.cjs",
+  "module": "src/module-importer.js",
   "type": "module",
   "types": "dist/module-importer.d.ts",
   "exports": {
-    "require": "./dist/module-importer.cjs",
-    "import": "./dist/module-importer.js"
+    "require": "./src/module-importer.cjs",
+    "import": "./src/module-importer.js"
   },
   "files": [
-    "dist"
+    "dist",
+    "src"
   ],
   "publishConfig": {
     "access": "public"

src/module-importer.cjs

@@ -0,0 +1,81 @@
+/**
+ * @fileoverview Universal module importer
+ */
+
+//-----------------------------------------------------------------------------
+// Imports
+//-----------------------------------------------------------------------------
+
+const { createRequire } = require("module");
+const { pathToFileURL }  = require("url");
+
+//-----------------------------------------------------------------------------
+// Helpers
+//-----------------------------------------------------------------------------
+
+const SLASHES = new Set(["/", "\\"]);
+
+/**
+ * Normalizes directories to have a trailing slash.
+ * Resolve is pretty finicky -- if the directory name doesn't have
+ * a trailing slash then it tries to look in the parent directory.
+ * i.e., if the directory is "/usr/nzakas/foo" it will start the 
+ * search in /usr/nzakas. However, if the directory is "/user/nzakas/foo/",
+ * then it will start the search in /user/nzakas/foo.
+ * @param {string} directory The directory to check. 
+ * @returns {string} The normalized directory.
+ */
+function normalizeDirectory(directory) {
+    if (!SLASHES.has(directory[directory.length-1])) {
+        return directory + "/";
+    }
+
+    return directory;
+}
+
+//-----------------------------------------------------------------------------
+// Exports
+//-----------------------------------------------------------------------------
+
+/**
+ * Class for importing both CommonJS and ESM modules in Node.js.
+ */
+exports.ModuleImporter = class ModuleImporter {
+
+    /**
+     * Creates a new instance.
+     * @param {string} [cwd] The current working directory to resolve from. 
+     */
+    constructor(cwd = process.cwd()) {
+
+        /**
+         * The base directory from which paths should be resolved.
+         * @type {string}
+         */
+        this.cwd = normalizeDirectory(cwd);
+    }
+
+    /**
+     * Resolves a module based on its name or location.
+     * @param {string} specifier Either an npm package name or
+     *      relative file path.
+     * @returns {string|undefined} The location of the import.
+     * @throws {Error} If specifier cannot be located.
+     */
+    resolve(specifier) {
+        const require = createRequire(this.cwd);
+        return require.resolve(specifier);
+    }
+
+    /**
+     * Imports a module based on its name or location.
+     * @param {string} specifier Either an npm package name or
+     *      relative file path.
+     * @returns {Promise<object>} The module's object.
+     */
+    import(specifier) {
+        const location = this.resolve(specifier);
+        return import(pathToFileURL(location).href);
+    }
+
+}

src/module-importer.js

@@ -7,75 +7,16 @@
 //-----------------------------------------------------------------------------
 
 import { createRequire } from "module";
-import { pathToFileURL } from "url";
+import { fileURLToPath } from "url";
+import { dirname } from "path";
 
 //-----------------------------------------------------------------------------
 // Helpers
 //-----------------------------------------------------------------------------
 
-const SLASHES = new Set(["/", "\\"]);
+const __filename = fileURLToPath(import.meta.url);
+const __dirname = dirname(__filename);
+const require = createRequire(__dirname + "/");
+const { ModuleImporter } = require("./module-importer.cjs");
 
-/**
- * Normalizes directories to have a trailing slash.
- * Resolve is pretty finicky -- if the directory name doesn't have
- * a trailing slash then it tries to look in the parent directory.
- * i.e., if the directory is "/usr/nzakas/foo" it will start the 
- * search in /usr/nzakas. However, if the directory is "/user/nzakas/foo/",
- * then it will start the search in /user/nzakas/foo.
- * @param {string} directory The directory to check. 
- * @returns {string} The normalized directory.
- */
-function normalizeDirectory(directory) {
-    if (!SLASHES.has(directory[directory.length-1])) {
-        return directory + "/";
-    }
-
-    return directory;
-}
-
-//-----------------------------------------------------------------------------
-// Exports
-//-----------------------------------------------------------------------------
-
-/**
- * Class for importing both CommonJS and ESM modules in Node.js.
- */
-export class ModuleImporter {
-
-    /**
-     * Creates a new instance.
-     * @param {string} [cwd] The current working directory to resolve from. 
-     */
-    constructor(cwd = process.cwd()) {
-
-        /**
-         * The base directory from which paths should be resolved.
-         * @type {string}
-         */
-        this.cwd = normalizeDirectory(cwd);
-    }
-
-    /**
-     * Resolves a module based on its name or location.
-     * @param {string} specifier Either an npm package name or
-     *      relative file path.
-     * @returns {string|undefined} The location of the import.
-     * @throws {Error} If specifier cannot be located.
-     */
-    resolve(specifier) {
-        const require = createRequire(this.cwd);
-        return require.resolve(specifier);
-    }
-
-    /**
-     * Imports a module based on its name or location.
-     * @param {string} specifier Either an npm package name or
-     *      relative file path.
-     * @returns {Promise<object>} The module's object.
-     */
-    import(specifier) {
-        const location = this.resolve(specifier);
-        return import(pathToFileURL(location).href);
-    }
-
-}
+export { ModuleImporter };

tests/pkg.test.cjs

@@ -3,5 +3,5 @@
  */
 
 const { ModuleImporter } = require("../");
-new ModuleImporter();
+(new ModuleImporter()).import("./src/module-importer.js");
 console.log("CommonJS load: success");