Add 'nodejs' buildback (Ref: rails/webpacker#739)

Procfile

@@ -1,2 +1,2 @@
-rails: rails server -p 3333
-webpack: ./bin/webpack-dev-server
+release: bin/rails db:migrate; ./bin/webpack-dev-server
+web: bin/rails server -p $PORT -e $RAILS_ENV

Procfile.dev

@@ -0,0 +1,2 @@
+rails: rails server -p 3333
+webpack: ./bin/webpack-dev-server

app.json

@@ -2,8 +2,7 @@
   "name": "elmsanity",
   "description": "",
   "scripts": {
-    "postdeploy": "cp config/database.yml.postgresql config/database.yml; bundle exec rails db:create; bundle exec rails db:migrate; NODE_ENV=production bundle exec rails webpacker:compile"
-  },
+},
   "env": {
     "SECRET_KEY_BASE": {
       "generator": "secret"
@@ -19,6 +18,7 @@
 
   ],
   "buildpacks": [
-
+    { "url": "heroku/nodejs" },
+    { "url": "heroku/ruby" }
   ]
 }

config/webpacker.yml

@@ -65,5 +65,15 @@ production:
 
 staging:
   <<: *default
-  compile: false
-  cache_manifest: true
+  compile: true
+  dev_server:
+    https: false
+    host: localhost
+    port: 3035
+    public: localhost:3035
+    hmr: false
+    # Inline should be set to true if using HMR
+    inline: true
+    overlay: true
+    disable_host_check: true
+    use_local_ip: false

package.json

@@ -5,10 +5,10 @@
     "@rails/webpacker": "^3.0.2",
     "coffeescript": "1.12.7",
     "elm": "^0.18.0",
-    "elm-webpack-loader": "^4.4.0"
+    "elm-webpack-loader": "^4.4.0",
+    "webpack-dev-server": "^2.9.4"
   },
   "devDependencies": {
-    "elm-hot-loader": "^0.5.4",
-    "webpack-dev-server": "^2.9.4"
+    "elm-hot-loader": "^0.5.4"
   }
 }