webpacker: ES6 syntax fails to compile even on a clean new app with --webpack=stimulus

ES6 syntax fails to compile even on a clean new app.

Expected Behavior

Run RAILS_ENV=production rake assets:precompile and get compiled assets without errors

Current Behavior

Uglifier::Error: Unexpected token: punc ({). To use ES6 syntax, harmony mode must be enabled with Uglifier.new(:harmony => true).

Steps to Reproduce

$ rails -v
-> Rails 5.1.5

$ rails new rails-stimulus-app --webpack=stimulus
$ cd rails-stimulus-app
$ RAILS_ENV=production rake assets:precompile --trace

Context (Environment)

Rails 5.1.5

# Gemfile
gem 'webpacker', '~> 3.2'

Detailed Description

$ rails -v
-> Rails 5.1.5

$ rails new rails-stimulus-app --webpack=stimulus
$ cd rails-stimulus-app
$ RAILS_ENV=production rake assets:precompile --trace

** Invoke assets:precompile (first_time)
** Invoke assets:environment (first_time)
** Execute assets:environment
** Invoke environment (first_time)
** Execute environment
** Invoke yarn:install (first_time)
** Execute yarn:install
yarn install v1.3.2
[1/4] 🔍  Resolving packages...
success Already up-to-date.
✨  Done in 0.59s.
** Execute assets:precompile
I, [2018-02-22T12:37:13.798156 #2626]  INFO -- : Writing /Users/joelsouza/Code/drafts/rails-stimulus-app/public/assets/application-4a1d9d80b89c980f5f64004484cb2e515409eb7565c72a78447d2c6be5636082.js
I, [2018-02-22T12:37:13.802969 #2626]  INFO -- : Writing /Users/joelsouza/Code/drafts/rails-stimulus-app/public/assets/application-4a1d9d80b89c980f5f64004484cb2e515409eb7565c72a78447d2c6be5636082.js.gz
I, [2018-02-22T12:37:13.810647 #2626]  INFO -- : Writing /Users/joelsouza/Code/drafts/rails-stimulus-app/public/assets/application-e3b0c44298fc1c149afbf4c8996fb92427ae41e4649b934ca495991b7852b855.css
I, [2018-02-22T12:37:13.810820 #2626]  INFO -- : Writing /Users/joelsouza/Code/drafts/rails-stimulus-app/public/assets/application-e3b0c44298fc1c149afbf4c8996fb92427ae41e4649b934ca495991b7852b855.css.gz
rake aborted!
Uglifier::Error: Unexpected token: punc ({). To use ES6 syntax, harmony mode must be enabled with Uglifier.new(:harmony => true).
/Users/joelsouza/.rbenv/versions/2.4.2/lib/ruby/gems/2.4.0/gems/uglifier-4.1.6/lib/uglifier.rb:234:in `parse_result'
/Users/joelsouza/.rbenv/versions/2.4.2/lib/ruby/gems/2.4.0/gems/uglifier-4.1.6/lib/uglifier.rb:216:in `run_uglifyjs'
/Users/joelsouza/.rbenv/versions/2.4.2/lib/ruby/gems/2.4.0/gems/uglifier-4.1.6/lib/uglifier.rb:168:in `compile'
/Users/joelsouza/.rbenv/versions/2.4.2/lib/ruby/gems/2.4.0/gems/sprockets-3.7.1/lib/sprockets/uglifier_compressor.rb:53:in `call'
/Users/joelsouza/.rbenv/versions/2.4.2/lib/ruby/gems/2.4.0/gems/sprockets-3.7.1/lib/sprockets/uglifier_compressor.rb:28:in `call'
/Users/joelsouza/.rbenv/versions/2.4.2/lib/ruby/gems/2.4.0/gems/sprockets-3.7.1/lib/sprockets/processor_utils.rb:75:in `call_processor'
/Users/joelsouza/.rbenv/versions/2.4.2/lib/ruby/gems/2.4.0/gems/sprockets-3.7.1/lib/sprockets/processor_utils.rb:57:in `block in call_processors'
/Users/joelsouza/.rbenv/versions/2.4.2/lib/ruby/gems/2.4.0/gems/sprockets-3.7.1/lib/sprockets/processor_utils.rb:56:in `reverse_each'
/Users/joelsouza/.rbenv/versions/2.4.2/lib/ruby/gems/2.4.0/gems/sprockets-3.7.1/lib/sprockets/processor_utils.rb:56:in `call_processors'
/Users/joelsouza/.rbenv/versions/2.4.2/lib/ruby/gems/2.4.0/gems/sprockets-3.7.1/lib/sprockets/loader.rb:134:in `load_from_unloaded'
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/Users/joelsouza/.rbenv/versions/2.4.2/lib/ruby/gems/2.4.0/gems/sprockets-3.7.1/lib/sprockets/loader.rb:317:in `fetch_asset_from_dependency_cache'
/Users/joelsouza/.rbenv/versions/2.4.2/lib/ruby/gems/2.4.0/gems/sprockets-3.7.1/lib/sprockets/loader.rb:44:in `load'
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/Users/joelsouza/.rbenv/versions/2.4.2/lib/ruby/gems/2.4.0/gems/sprockets-3.7.1/lib/sprockets/cached_environment.rb:47:in `load'
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/Users/joelsouza/.rbenv/versions/2.4.2/lib/ruby/gems/2.4.0/gems/sprockets-3.7.1/lib/sprockets/base.rb:73:in `find_all_linked_assets'
/Users/joelsouza/.rbenv/versions/2.4.2/lib/ruby/gems/2.4.0/gems/sprockets-3.7.1/lib/sprockets/manifest.rb:142:in `block in find'
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/Users/joelsouza/.rbenv/versions/2.4.2/lib/ruby/gems/2.4.0/gems/sprockets-3.7.1/lib/sprockets/path_utils.rb:228:in `block in stat_tree'
/Users/joelsouza/.rbenv/versions/2.4.2/lib/ruby/gems/2.4.0/gems/sprockets-3.7.1/lib/sprockets/path_utils.rb:212:in `block in stat_directory'
/Users/joelsouza/.rbenv/versions/2.4.2/lib/ruby/gems/2.4.0/gems/sprockets-3.7.1/lib/sprockets/path_utils.rb:209:in `each'
/Users/joelsouza/.rbenv/versions/2.4.2/lib/ruby/gems/2.4.0/gems/sprockets-3.7.1/lib/sprockets/path_utils.rb:209:in `stat_directory'
/Users/joelsouza/.rbenv/versions/2.4.2/lib/ruby/gems/2.4.0/gems/sprockets-3.7.1/lib/sprockets/path_utils.rb:227:in `stat_tree'
/Users/joelsouza/.rbenv/versions/2.4.2/lib/ruby/gems/2.4.0/gems/sprockets-3.7.1/lib/sprockets/path_utils.rb:231:in `block in stat_tree'
/Users/joelsouza/.rbenv/versions/2.4.2/lib/ruby/gems/2.4.0/gems/sprockets-3.7.1/lib/sprockets/path_utils.rb:212:in `block in stat_directory'
/Users/joelsouza/.rbenv/versions/2.4.2/lib/ruby/gems/2.4.0/gems/sprockets-3.7.1/lib/sprockets/path_utils.rb:209:in `each'
/Users/joelsouza/.rbenv/versions/2.4.2/lib/ruby/gems/2.4.0/gems/sprockets-3.7.1/lib/sprockets/path_utils.rb:209:in `stat_directory'
/Users/joelsouza/.rbenv/versions/2.4.2/lib/ruby/gems/2.4.0/gems/sprockets-3.7.1/lib/sprockets/path_utils.rb:227:in `stat_tree'
/Users/joelsouza/.rbenv/versions/2.4.2/lib/ruby/gems/2.4.0/gems/sprockets-3.7.1/lib/sprockets/path_utils.rb:231:in `block in stat_tree'
/Users/joelsouza/.rbenv/versions/2.4.2/lib/ruby/gems/2.4.0/gems/sprockets-3.7.1/lib/sprockets/path_utils.rb:212:in `block in stat_directory'
/Users/joelsouza/.rbenv/versions/2.4.2/lib/ruby/gems/2.4.0/gems/sprockets-3.7.1/lib/sprockets/path_utils.rb:209:in `each'
/Users/joelsouza/.rbenv/versions/2.4.2/lib/ruby/gems/2.4.0/gems/sprockets-3.7.1/lib/sprockets/path_utils.rb:209:in `stat_directory'
/Users/joelsouza/.rbenv/versions/2.4.2/lib/ruby/gems/2.4.0/gems/sprockets-3.7.1/lib/sprockets/path_utils.rb:227:in `stat_tree'
/Users/joelsouza/.rbenv/versions/2.4.2/lib/ruby/gems/2.4.0/gems/sprockets-3.7.1/lib/sprockets/path_utils.rb:231:in `block in stat_tree'
/Users/joelsouza/.rbenv/versions/2.4.2/lib/ruby/gems/2.4.0/gems/sprockets-3.7.1/lib/sprockets/path_utils.rb:212:in `block in stat_directory'
/Users/joelsouza/.rbenv/versions/2.4.2/lib/ruby/gems/2.4.0/gems/sprockets-3.7.1/lib/sprockets/path_utils.rb:209:in `each'
/Users/joelsouza/.rbenv/versions/2.4.2/lib/ruby/gems/2.4.0/gems/sprockets-3.7.1/lib/sprockets/path_utils.rb:209:in `stat_directory'
/Users/joelsouza/.rbenv/versions/2.4.2/lib/ruby/gems/2.4.0/gems/sprockets-3.7.1/lib/sprockets/path_utils.rb:227:in `stat_tree'
/Users/joelsouza/.rbenv/versions/2.4.2/lib/ruby/gems/2.4.0/gems/sprockets-3.7.1/lib/sprockets/path_utils.rb:231:in `block in stat_tree'
/Users/joelsouza/.rbenv/versions/2.4.2/lib/ruby/gems/2.4.0/gems/sprockets-3.7.1/lib/sprockets/path_utils.rb:212:in `block in stat_directory'
/Users/joelsouza/.rbenv/versions/2.4.2/lib/ruby/gems/2.4.0/gems/sprockets-3.7.1/lib/sprockets/path_utils.rb:209:in `each'
/Users/joelsouza/.rbenv/versions/2.4.2/lib/ruby/gems/2.4.0/gems/sprockets-3.7.1/lib/sprockets/path_utils.rb:209:in `stat_directory'
/Users/joelsouza/.rbenv/versions/2.4.2/lib/ruby/gems/2.4.0/gems/sprockets-3.7.1/lib/sprockets/path_utils.rb:227:in `stat_tree'
/Users/joelsouza/.rbenv/versions/2.4.2/lib/ruby/gems/2.4.0/gems/sprockets-3.7.1/lib/sprockets/path_utils.rb:231:in `block in stat_tree'
/Users/joelsouza/.rbenv/versions/2.4.2/lib/ruby/gems/2.4.0/gems/sprockets-3.7.1/lib/sprockets/path_utils.rb:212:in `block in stat_directory'
/Users/joelsouza/.rbenv/versions/2.4.2/lib/ruby/gems/2.4.0/gems/sprockets-3.7.1/lib/sprockets/path_utils.rb:209:in `each'
/Users/joelsouza/.rbenv/versions/2.4.2/lib/ruby/gems/2.4.0/gems/sprockets-3.7.1/lib/sprockets/path_utils.rb:209:in `stat_directory'
/Users/joelsouza/.rbenv/versions/2.4.2/lib/ruby/gems/2.4.0/gems/sprockets-3.7.1/lib/sprockets/path_utils.rb:227:in `stat_tree'
/Users/joelsouza/.rbenv/versions/2.4.2/lib/ruby/gems/2.4.0/gems/sprockets-3.7.1/lib/sprockets/legacy.rb:105:in `each'
/Users/joelsouza/.rbenv/versions/2.4.2/lib/ruby/gems/2.4.0/gems/sprockets-3.7.1/lib/sprockets/legacy.rb:105:in `block in logical_paths'
/Users/joelsouza/.rbenv/versions/2.4.2/lib/ruby/gems/2.4.0/gems/sprockets-3.7.1/lib/sprockets/legacy.rb:104:in `each'
/Users/joelsouza/.rbenv/versions/2.4.2/lib/ruby/gems/2.4.0/gems/sprockets-3.7.1/lib/sprockets/legacy.rb:104:in `logical_paths'
/Users/joelsouza/.rbenv/versions/2.4.2/lib/ruby/gems/2.4.0/gems/sprockets-3.7.1/lib/sprockets/manifest.rb:140:in `find'
/Users/joelsouza/.rbenv/versions/2.4.2/lib/ruby/gems/2.4.0/gems/sprockets-3.7.1/lib/sprockets/manifest.rb:185:in `compile'
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/Users/joelsouza/.rbenv/versions/2.4.2/lib/ruby/2.4.0/monitor.rb:214:in `mon_synchronize'
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/Users/joelsouza/.rbenv/versions/2.4.2/bin/rake:23:in `load'
/Users/joelsouza/.rbenv/versions/2.4.2/bin/rake:23:in `<main>'
Tasks: TOP => assets:precompile