Concatenating first vs concatenating last performance comparison

benchmark.rb

environment = Rails.application.assets
asset = nil

environment.send :expire_index!
FileUtils.rm_rf environment.cache.instance_variable_get :@root

puts Benchmark.measure{File.write '/tmp/application-orig.js', (asset = environment['application']).source}.total

puts(Benchmark.measure do

cs_source = []
js_source = []

i = -1
asset.to_a.each do |d|
  if File.extname(d.pathname.to_s) == '.coffee'
    cs_source.push "do ->\n", d.pathname.read.gsub(/^(.)/, ' \\1')
  else
    cs_source.push "`class({{#{i += 1}}})`;"
    js_source.push d.body
  end
end

s=CoffeeScript.compile(cs_source.join)
File.write '/tmp/application.js', js_source.each.with_index.inject(s){|a, (v, i)| a.sub("class({{#{i}}});"){v} }

end.total)

results.txt

EXECJS_RUNTIME = Node:
9.9
1.7

EXECJS_RUNTIME = RubyRacer:
2.3
2.5