I just started with the In-App scripting using JS. One nice source to learn and understand the syntax is the JavaScript Command library provided under https://dlubal-software.github.io/.github/. Using this library I noticed two issues:
Possible input options and their syntax for params are missing. For example, if you want to find out how to input the magnitude or direction of a line load, you need to browse the example files and sometimes guess suitable input values. It would be nice if the params input options for a specific command would be listed in the library.