Single babel config

app/frontend/application.js

@@ -2,17 +2,17 @@
 // present in this directory. You're encouraged to place your actual application logic in
 // a relevant structure within app/javascript and only use these pack files to reference
 // that code so it'll be compiled.
-require.context("govuk-frontend/govuk/assets")
 
 // Polyfills for IE
-import "core-js/features/promise"
+import "regenerator-runtime/runtime"
-import "unfetch/polyfill"
 import "@stimulus/polyfills"
+import "custom-event-polyfill"
 //
 
+require.context("govuk-frontend/govuk/assets")
+import { initAll } from "govuk-frontend"
 import "./styles/application.scss"
 import "./controllers"
 import "@hotwired/turbo-rails"
-import { initAll } from "govuk-frontend"
 
 initAll()

babel.config.js

@@ -41,6 +41,18 @@ module.exports = function(api) {
           loose: true
         }
       ],
+      [
+        "@babel/plugin-proposal-private-methods",
+        {
+          loose: true
+        }
+      ],
+      [
+        "@babel/plugin-proposal-private-property-in-object",
+        {
+          loose: true
+        }
+      ],
       [
         '@babel/plugin-proposal-object-rest-spread',
         {

package.json

@@ -21,6 +21,7 @@
     "copy-webpack-plugin": "^10.2.4",
     "core-js": "^3.21.1",
     "css-loader": "^6.7.1",
+    "custom-event-polyfill": "^1.0.7",
     "file-loader": "^6.2.0",
     "govuk-frontend": "^4.0.1",
     "mini-css-extract-plugin": "^2.6.0",
@@ -46,15 +47,6 @@
       "last 1 safari version"
     ]
   },
-  "babel": {
-    "presets": [
-      "@babel/preset-env"
-    ],
-    "plugins": [
-      "@babel/plugin-proposal-class-properties",
-      "@babel/plugin-proposal-private-methods"
-    ]
-  },
   "scripts": {
     "build": "webpack --config webpack.config.js"
   }

yarn.lock

@@ -1519,6 +1519,11 @@ cssesc@^3.0.0:
   resolved "https://registry.yarnpkg.com/cssesc/-/cssesc-3.0.0.tgz#37741919903b868565e1c09ea747445cd18983ee"
   integrity sha512-/Tb/JcjK111nNScGob5MNtsntNM1aCNUDipB/TkwZFhyDrrE47SOx/18wF2bbjgc3ZzCSKW1T5nt5EbFoAz/Vg==
 
+custom-event-polyfill@^1.0.7:
+  version "1.0.7"
+  resolved "https://registry.yarnpkg.com/custom-event-polyfill/-/custom-event-polyfill-1.0.7.tgz#9bc993ddda937c1a30ccd335614c6c58c4f87aee"
+  integrity sha512-TDDkd5DkaZxZFM8p+1I3yAlvM3rSr1wbrOliG4yJiwinMZN8z/iGL7BTlDkrJcYTmgUSb4ywVCc3ZaUtOtC76w==
+
 date-fns@>=2.0.0:
   version "2.28.0"
   resolved "https://registry.yarnpkg.com/date-fns/-/date-fns-2.28.0.tgz#9570d656f5fc13143e50c975a3b6bbeb46cd08b2"