javascript - Firefox Extension: self.port.on not passing result to outer function

main.js

var tURL;
var self = require("sdk/self");
var tabs = require("sdk/tabs");
var data = self.data;


/*
contentScriptFile: [data.url("scripts/lib/jquery.js"),
                    data.url("scripts/lib/jquery-ui.js"),
                    data.url("scripts/platform.js")];
*/
// First time install
if (require('sdk/self').loadReason == 'install') {
  // Do something on the very first install
  tabs.open("http://www.example.com/test2.php");

}

require("sdk/tabs").on("ready", logURL);
function logURL(tab) {
  tURL = tab.url;
  console.log("LOGURL: "+tURL);

  var worker = tabs.activeTab.attach({
    contentScriptFile: [data.url("scripts/lib/jquery.js"),
                        data.url("scripts/platform.js"),

                        data.url("scripts/script.js")]
  });
  worker.port.emit("vsAPI", tURL);


  worker.port.on('getURL', function(callback) {
    var gotURL = data.url(callback);
    worker.port.emit("gotURL", gotURL);
  });


}

platform.js

function Platform() {
  var that = this;

  that.getURL = function (filename) {


    self.port.emit('getURL', filename);

    self.port.on("gotURL", function(callback) {
      console.log("gotURL: "+callback);
      var output = callback;
    });
    //console.log("output: "+output);
    return output;

  }

}

Problem:

platform.js emits to main.js

main.js receives, processes and passes back result to platform.js

platform.js receives result successfully.

However, I want to use the result outside of the port.on function...

I.E:

self.port.on("gotURL", function(callback) {
  console.log("gotURL: "+callback);
  var output = callback;
});

I want to use "var output" outside of self.port.on("gotURL")

Any ideas what I need to tweak please?

Thanks!