feat(esm): try and be a bit smarter about ESM generation

package.json

@@ -1,6 +1,6 @@
 {
   "name": "coconfig",
-  "version": "1.1.0",
+  "version": "1.2.0",
   "description": "Centralize your per-package rc, dotfile and config files into one extensible config file",
   "main": "build/index.js",
   "types": "build/index.d.ts",

src/bin/cli.ts

@@ -21,7 +21,7 @@ async function run() {
   const pkgInfo = readPkgUp.sync({ cwd: argv.cwd, normalize: argv.normalize });
   assert(pkgInfo, 'Cannot find package.json. Pass cwd option that points to a directory with a package.json');
   const { packageJson, path } = pkgInfo;
-  const pkgValue = packageJson.config?.coconfig;
+  const pkgValue = packageJson.config?.coconfig as string | undefined;
   const { coconfigPath, config } = await resolveConfig(path, pkgValue);
 
   const coconfigEnv: CoConfigEnvironment = {

src/passthrough.ts

@@ -30,22 +30,21 @@ function getModulePath(configRef: string) {
   return configRef;
 }
 
-export function getFile(
-  env: CoConfigEnvironment,
-  key: string,
-  filename: string,
-) {
+export function getFile(env: CoConfigEnvironment, key: string, filename: string) {
   const configRef = configReference(env.coconfigPath, env.packagePath);
-  const modulePath = getModulePath(configRef);
+  const isModule = env.packageJson?.type === 'module' || /.m[jt]s/.test(path.extname(filename));
+
+  const modulePath = isModule ? configRef : getModulePath(configRef);
+
+  const isTs = /\.[mc]?ts/.test(path.extname(filename));
 
   const commonCode = `
 const configItem = configModule.default || configModule.config || configModule;
 const { configuration } = configItem && configItem['${key}'];
 const resolved = typeof configuration === 'function' ? configuration() : configuration;
 `;
 
-  if (path.extname(filename) === '.ts') {
-    // Target is Typescript
+  if (isModule && isTs) {
     return `${header}
 import cjs from '${modulePath}';
 import * as esmToCjs from '${modulePath}';
@@ -56,6 +55,18 @@ ${commonCode}
 // eslint-disable-next-line import/no-default-export
 export default resolved;\n`;
   }
+
+  if (isModule) {
+    return `${header}
+import cjs from '${modulePath}';
+import * as esmToCjs from '${modulePath}';
+
+const configModule = cjs || esmToCjs;
+${commonCode}
+// eslint-disable-next-line import/no-default-export
+export default resolved;\n`;
+  }
+
   if (path.extname(env.coconfigPath) === '.ts') {
     // Target is JS, source is typescript (requires ts-node)
     return `${header}

src/resolver.ts

@@ -21,6 +21,10 @@ function getExport(module: Record<string, unknown>) {
   return module;
 }
 
+/**
+ * Try and dynamically load a coconfig file in a variety of
+ * environments - esm, cjs, ts, js, cjs esm, etc.
+ */
 async function load(coconfigPath: string): Promise<{ coconfigPath: string; config: CoConfigFile }> {
   try {
     if (path.extname(coconfigPath) === '.ts') {
@@ -45,7 +49,7 @@ async function load(coconfigPath: string): Promise<{ coconfigPath: string; confi
   }
 }
 
-export async function resolveConfig(pkgPath: string, pkgValue?: any) {
+export async function resolveConfig(pkgPath: string, pkgValue?: string) {
   if (typeof pkgValue === 'string') {
     if (pkgValue.startsWith('.')) {
       return load(path.resolve(path.dirname(pkgPath), pkgValue));