Port relevant tests to Jest

.npmrc

@@ -0,0 +1,3 @@
+# Jest uses the `vm` module, which does not have production ready module support
+# yet. This option lets us use dynamic imports.
+node-options='--experimental-vm-modules'

jest.config.js

@@ -0,0 +1,24 @@
+/** @type {import('jest').Config} */
+module.exports = {
+  moduleDirectories: [
+    "node_modules",
+    "build/js",
+  ],
+  transform: {
+    // Most of the build outputs in this project use UMD syntax, but the
+    // utilities script is a proper ES Module. Unfortunately, Jest cannot treat
+    // a file with a `.js` extension as ESM unless the whole project is ESM
+    // (Jest does not use Node.js built-in resolution and loading logic), so
+    // we have to set up special parsing for that file.
+    // See also: https://jestjs.io/docs/next/ecmascript-modules
+    "utils.js$": [
+      "babel-jest",
+      {
+        plugins: [
+          "@babel/plugin-transform-modules-commonjs",
+          "babel-plugin-add-module-exports",
+        ],
+      },
+    ],
+  },
+};

package.json

@@ -24,13 +24,15 @@
   "license": "MIT",
   "author": "Jack O'Connor (http://jackocnr.com)",
   "devDependencies": {
+    "@babel/plugin-transform-modules-commonjs": "^7.25.7",
     "@testing-library/jest-dom": "^6.4.6",
     "@testing-library/user-event": "^14.5.2",
     "@types/react": "^18.2.74",
     "@types/react-dom": "^18.2.24",
     "@typescript-eslint/eslint-plugin": "^8.1.0",
     "@typescript-eslint/parser": "^8.1.0",
     "@vitejs/plugin-vue": "^5.1.2",
+    "babel-plugin-add-module-exports": "^1.0.4",
     "cspell": "^8.6.1",
     "esbuild": "^0.23.0",
     "eslint": "^8.57.0",
@@ -152,11 +154,5 @@
         "react/build/IntlTelInput.d.ts"
       ]
     }
-  },
-  "jest": {
-    "moduleDirectories": [
-      "node_modules",
-      "build/js"
-    ]
   }
 }

spec.html

@@ -72,8 +72,6 @@
 
   <script src="src/spec/tests/options/initialCountry.js"></script>
 
-  <script src="src/spec/tests/options/loadUtilsOnInit.js"></script>
-
   <script src="src/spec/tests/options/nationalMode.js"></script>
 
   <script src="src/spec/tests/options/onlyCountries.js"></script>
@@ -88,8 +86,6 @@
 
   <script src="src/spec/tests/static/getCountryData.js"></script>
 
-  <script src="src/spec/tests/static/loadUtils.js"></script>
-
   <script src=".grunt/grunt-contrib-jasmine/reporter.js"></script>