PackR is a Ruby port of Dean Edwards’ JavaScript compressor

Compressing javascript files is one way you can quickly speed up a sluggish web app. I have seen ratios approaching 1.8 in some cases of very long variable names. Renaming variables that are only used in local scope is safe, and will reduce overall file size...Although not the end all solution for all problems, it should be in your bag of tricks.

PackR

PackR is a Ruby port of Dean Edwards’ MIT-licensed JavaScript compressor, Packer. It is made available as a plugin for Ruby on Rails.
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PackR also comes with a rake task to let you batch-pack all your scripts. To use it, store any files you want to serve in packed form in the directory lib/javascripts. (The idea is that you won‘t be serving the source files to the public, so why keep them in the public folder? Also, it keeps the source files and packed copies nicely separated.)