Fix incorrect ESM build configuration

.github/workflows/jest.yaml

@@ -8,7 +8,7 @@ jobs:
             - name: Setup Node.js
               uses: actions/setup-node@v1
               with:
-                  node-version: "18"
+                  node-version: "22"
 
             - name: Install dependencies
               run: npm install

.github/workflows/lint.yaml

@@ -8,7 +8,7 @@ jobs:
             - name: Setup Node.js
               uses: actions/setup-node@v1
               with:
-                  node-version: "18"
+                  node-version: "22"
 
             - name: Install dependencies
               run: npm install

CHANGELOG.md

@@ -5,6 +5,12 @@ All notable changes to this project will be documented in this file.
 The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/),
 and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
 
+## [Unreleased]
+
+### Fixed
+
+- Fix incorrect ESM build configuration leading to broken build output
+
 ## [0.30.0] - 2025-11-28
 
 ### Added

eslint.config.mjs

@@ -1,6 +1,7 @@
 import { defineConfig } from 'eslint/config'
 import globals from 'globals'
 import tseslint from 'typescript-eslint'
+import importPlugin from 'eslint-plugin-import'
 
 export default defineConfig([
   { files: ['src/**/*.{ts}', 'tests/**/*.{ts}'] },
@@ -15,4 +16,25 @@ export default defineConfig([
       '@typescript-eslint/no-unused-vars': 'warn',
     },
   },
+  {
+    files: ['src/**/*.ts'],
+    plugins: {
+      import: importPlugin,
+    },
+    rules: {
+      // assert relative imports always have .ts extension
+      'import/extensions': [
+        'error',
+        'ignorePackages',
+        {
+          ts: 'always',
+          tsx: 'never',
+          js: 'never',
+          jsx: 'never',
+          mjs: 'never',
+          cjs: 'never',
+        },
+      ],
+    },
+  },
 ])

jest.config.ts

@@ -9,6 +9,10 @@ const jestConfig: Config = {
   transform: {
     '^.+\\.ts$': 'ts-jest',
   },
+  moduleNameMapper: {
+    '^(\\.{1,2}/.*)\\.ts$': '$1',
+    '^(\\.{1,2}/.*)\\.js$': '$1',
+  },
 }
 
 export default jestConfig