WebApplication.Port

From Xojo Documentation

Read-Only Property (As Integer )
IntegerValue = aWebApplication.Port

New in 2010r4

Supported for all project types and targets.

The port number used to communicate with the standalone web app when it is built and deployed.

Notes

In addition to being set in the Build Settings for the web app, this value can also be set at launch time by appending the --port command line parameter.

Usage:

MyApp --port=9000

On macOS and Linux, port numbers below 1024 (including the common port 80) require elevated permissions, so you will have to start the web app using the "sudo" command.