Enforce file extensions in imports to comply with ESM standards (#486)

Author: dmz-v-x

.eslintrc.cjs

@@ -33,12 +33,20 @@ module.exports = {
         'vue/no-reserved-component-names': 0,
         'eol-last': ['error', 'always'],
         'prettier/prettier': 'error',
+        'import/extensions': [
+            'error',
+            'always',
+            {
+                js: 'always',
+                vue: 'always',
+            },
+        ],
     },
     globals: {
         describe: true,
         expect: true,
         it: true,
         test: true,
     },
-    plugins: ['prettier'],
+    plugins: ['prettier', 'import'],
 };