I'm learning to write JavaScript in the modern Forms designer.

I have a collection with two drop-down controls for grade and school. When a user selects a grade, I want to set the school dropdown to list the schools that offer that grade. For example, if the user selects grade 6, the school dropdown should be populated with all the schools that offer grade 6.

I've created an event handler and called it using subscribe and using onFieldChange. That worked in that the handler got called when expected. Unfortunately, I wasn't able to determine in the handler, which instance of the grade control had been changed. I found the argument that got passed to the handler, but that didn't help. The argument includes a variable named "Index", but it is set to null.

Is what I'm trying to do possible? If so, I'd love to get ideas on how to do it.

Thank you!