namespace :webpack do
  desc "Compile webpack bundles"
  task compile: :environment do
    ENV["TARGET"] = 'production' # TODO: Deprecated, use NODE_ENV instead
    ENV["NODE_ENV"] ||= 'production'
    webpack_bin = ::Rails.root.join(::Rails.configuration.webpack.binary)
    config_file = ::Rails.root.join(::Rails.configuration.webpack.config_file)

    unless File.exist?(webpack_bin)
      raise "Can't find our webpack executable at #{webpack_bin} - have you run `npm install`?"
    end

    unless File.exist?(config_file)
      raise "Can't find our webpack config file at #{config_file}"
    end

    sh "#{webpack_bin} --config #{config_file} --bail"
  end
end

namespace :webpack do
  desc "Compile webpack bundles"
  task compile: :environment do
    ENV["TARGET"] = 'production' # TODO: Deprecated, use NODE_ENV instead
    ENV["NODE_ENV"] = 'production'
    webpack_bin = ::Rails.root.join(::Rails.configuration.webpack.binary)
    config_file = ::Rails.root.join(::Rails.configuration.webpack.config_file)

    unless File.exist?(webpack_bin)
      raise "Can't find our webpack executable at #{webpack_bin} - have you run `npm install`?"
    end

    unless File.exist?(config_file)
      raise "Can't find our webpack config file at #{config_file}"
    end

    sh "#{webpack_bin} --config #{config_file} --bail"
  end
end

--- 
+++ 
@@ -2,7 +2,7 @@
   desc "Compile webpack bundles"
   task compile: :environment do
     ENV["TARGET"] = 'production' # TODO: Deprecated, use NODE_ENV instead
-    ENV["NODE_ENV"] = 'production'
+    ENV["NODE_ENV"] ||= 'production'
     webpack_bin = ::Rails.root.join(::Rails.configuration.webpack.binary)
     config_file = ::Rails.root.join(::Rails.configuration.webpack.config_file)
 
Use existing NODE_ENV if available