This library was created in order to provide a reasonably fast Javascript
minifier on JRuby platform.
Both native Java and Ruby implementations were found to be in several orders
of magnitude slower.
The only change from the original C implementation, is that it was changed
to C++ (in order to make global variables become instance variables),
and it works with buffers rather than stdin/stdout now.

 require 'jsmin_ffi'
 input = IO.read('prototype.js')
 begin
   output = JsminFFI.minify!(input)
   File.open('output.js', 'w') {|f| f.write(output)}
 rescue Jsmin::ParseError => e
   $stderr.puts "Cannot minify: #{e}"
 end

or use a native extension:

 require ‘Jsmin’

 input = IO.read(‘jquery.js’)

 begin

   output = Jsmin.minify(input)

   File.open(‘output.js’, ‘w’) {|f| f.write(output)}

 rescue Jsmin::ParseError => e

   $stderr.puts “Cannot minify: #{e}”

 end

The memory allocated in the C++ code might not be freed when using FFI.
It depends on how FFI handles the returned char*.

For the original implementation, please see:
http://www.crockford.com/javascript/jsmin.html