Uglify the global variable

I have an app in nodejs. In it, I define some global variables that are shared across multiple files. For example:

//common.jsasync = requires("async");isAuthenticated = function() {  //...  return false;};//run.jsrequire("common.js");async.series([function () {  isAuthenicated();}], function () {  console.log("done");});

I want the async and isAuthenticated variables to be minified, but minified to the same thing in all files. It would look like the following:

//common.min.jsa = requires("async");b = function() {  //...  return false;};//run.min.jsrequire("common.js");a.series([function () {  b();}], function () {  console.log("done");});

How to do it in uglifyjs?

I'm currently looping through the files and using the command uglifyjs $file -m "sort,toplevel" -c > $file.min on each.