When I run the code, it's like it's ignoring the call. If I plug the URL from the Developer tools into a browser, it just sits and spins. I can see the encoded value for itemNumber in the URL.
Browsers have debuggers, network monitors, etc built in to assist with debugging applications. I would suggest using these tools to learn a little more about what's failing:
1. Look at the network requests made. Are they being made when you expect? Is the data sent what you expect it to be?
2. Is the JavaScript code crashing? Is there an error message in the console that explains what's wrong?
3. Is the JavaScript not crashing, and the network request being sent properly -- but not getting any response? If so, what is happening on the server-side? Is the UDF program crashing? Are there errors in the job log?
It'd help an awful lot to narrow down what's happening... the more information you provide, the more likely we'll be able to help you.