I use UglifyJS which is not only written in JavaScript but uses NodeJS (a backend JavaScript programming language) to compress your JavaScript files. For me it was a tossup between using Google Closure or Uglify and research showed that Uglify/Node was faster and led to slightly small files. Libraries like jQuery have also moved to Uglify.
Setting up UglifyJS is not that hard. You don't need to know Node to use it (though if you know JavaScript you pretty much know Node already). UglifyJS comes as both a shell utility and a Node js library you can import and use in your Node script. I went ahead and did the later as diving into Node was fun, but you could also write a php script to drop down to shell and use the Node shell utility. You do need to compile Node for your server in either situation, though (which also installs the V8 JavaScript engine).
Once you have Node installs you could do additional fun things like setup jshint to validate your JS on your server.