fix: Add missing js dependencies

Rakefile

@@ -2,8 +2,23 @@
 
 require "decidim/dev/common_rake"
 
+def js_configuration(path)
+  babel_file_path = File.join(Dir.pwd, "babel.config.json")
+
+  Dir.chdir(path) do
+    FileUtils.cp(babel_file_path, "babel.config.json")
+    system("yarn add @babel/plugin-proposal-private-methods")
+    system("yarn add @babel/plugin-proposal-private-property-in-object")
+  end
+end
+
 desc "Generates a dummy app for testing"
-task test_app: "decidim:generate_external_test_app"
+task test_app: "decidim:generate_external_test_app" do
+  ENV["RAILS_ENV"] = "test"
+  js_configuration("spec/decidim_dummy_app")
+end
 
 desc "Generates a development app."
-task development_app: "decidim:generate_external_development_app"
+task development_app: "decidim:generate_external_development_app" do
+  js_configuration("development_app")
+end

babel.config.json

@@ -0,0 +1,28 @@
+{
+  "presets": [
+    [
+      "@babel/preset-env", {
+        "forceAllTransforms": true,
+        "useBuiltIns": "entry",
+        "corejs": 3,
+        "modules": false
+      }
+    ],
+    ["@babel/preset-react"]
+  ],
+  "plugins": [
+    "@babel/plugin-transform-classes",
+    [
+      "@babel/plugin-transform-runtime",
+      {
+        "helpers": false,
+        "regenerator": true,
+        "corejs": false
+      }
+    ],
+    [ "@babel/plugin-transform-regenerator", { "async": false }],
+    [ "@babel/plugin-proposal-private-property-in-object", { "loose": true }],
+    ["@babel/plugin-proposal-private-methods", { "loose": true }],
+    ["@babel/plugin-proposal-class-properties", { "loose": true }]
+  ]
+}

yarn.lock

@@ -0,0 +1,4 @@
+# THIS IS AN AUTOGENERATED FILE. DO NOT EDIT THIS FILE DIRECTLY.
+# yarn lockfile v1
+
+