Install Webpacker

Gemfile

@@ -110,3 +110,5 @@ group :development, :test do
   gem 'rails-controller-testing'
   gem 'haml_lint', require: false
 end
+
+gem "webpacker", "~> 5.2"

Gemfile.lock

@@ -363,6 +363,8 @@ GEM
       rack (>= 1.1)
     rack-protection (2.1.0)
       rack
+    rack-proxy (0.6.5)
+      rack
     rack-test (1.1.0)
       rack (>= 1.0, < 3)
     rails (5.2.4.4)
@@ -492,6 +494,7 @@ GEM
       sprockets (> 3.0)
       sprockets-rails
       tilt
+    semantic_range (2.3.1)
     shellany (0.0.1)
     sidekiq (5.2.9)
       connection_pool (~> 2.2, >= 2.2.2)
@@ -554,6 +557,11 @@ GEM
       activemodel (>= 5.0)
       bindex (>= 0.4.0)
       railties (>= 5.0)
+    webpacker (5.2.1)
+      activesupport (>= 5.2)
+      rack-proxy (>= 0.6.1)
+      railties (>= 5.2)
+      semantic_range (>= 2.3.0)
     websocket-driver (0.7.3)
       websocket-extensions (>= 0.1.0)
     websocket-extensions (0.1.5)
@@ -645,6 +653,7 @@ DEPENDENCIES
   twitter
   uglifier (>= 1.3.0)
   web-console (< 4.0.0)
+  webpacker (~> 5.2)
 
 BUNDLED WITH
    2.1.4