Using Javascript in Mongoose

You use C# or VB

I am using C#

I'm not certain what restrictions there may be in MT, but depending on what you're needing to do, you probably want to look at web user controls - https://docs.infor.com/mg/2024.x/en-us/mongooseolh/default.html?helpcontent=mgwsolh_mg/lsm1454148028518.html

I would agree with the sentiment that if you can, you should do what you need to in form or global script if at all possible.