Exclude any js file from uglifier optimization during assets:precompile

If you need to exclude a file from optimization by UglifyJS when you run rake assets:precompile, you can use this custom class. (Modify it for your own needs)

Place this class into any suitable folder (e.g. lib/ext).

class ConditionalUglifier < Uglifier
  def really_compile(source, generate_map)
    # Skip any optimization (e.g. for shims)
    if source =~ /^\/\/= skip/
      source.gsub!(/\/\/= ?skip(\n)*;(\n)*\z/, "")
    else
      super
    end
  end
end

Require it in production.rb (if it's needed) and specify ConditionalUglifier as your js_compressor.

require 'ext/conditional_uglifier'

# Compress JavaScripts and CSS.
config.assets.js_compressor = ConditionalUglifier.new

Add //= skip to the first line of any js file that you want to exclude from the optimization.
An example of shim.js:

//= skip
//= require shims/classList.min
//= require shims/raf.min
//= require shims/weakmap.min