Use UglifyJS 2 (uglify-js package) to compress a string of JavaScript source code

uglify.js

var UglifyJS = require('uglify-js');

module.exports = function(code) {
  var toplevel = UglifyJS.parse(code);

  toplevel.figure_out_scope();

  var compressor = UglifyJS.Compressor({
    warnings: false
  });
  var compressed = toplevel.transform(compressor);

  compressed.figure_out_scope();
  compressed.compute_char_frequency();
  compressed.mangle_names();

  return compressed.print_to_string();
}