app dialogs were succeeded by SUI about a decade ago, SUI is in it's dying stages, app dialogs are already dead.
Either use SUI or Work on CS6 were your code will work.
Thanks Trevor. That's very helpful. The only books I could find to teach me are more than ten years old. Are there likely to be other areas where the code is obsolete?
There are several DOM elements that have changed or been depreciated or introduced, there are lists of some of the changes.
I would recommend peter kahrel guides, SUI and GREP guides are excellent, he has on general InDesign scripting as well which I have not read but it's likely to be good too.
The adobe js manual is particularly useful as are the references here Where to locate the latest Indesign CC scripting documentation ?
For more advanced stuff there the toolkit guide see the link for more details
Awesome, will check out those links. Thanks so much for taking the time to help me along my way, much appreciated!