How to detect "required" field property in form?

Hello all - new to these forums and to Javascript, but long-time programmer, in an unfamiliar environment. I'm trying to figure out how to detect, in Javascript, whether a field is marked as "required" in its properties. I've been googling my brains out and banging out code for hours and can't figure it out.

I assumed a simple loop through the document's fields testing for a ".required" property would do it, but the simple test below fails with the message "InvalidGetError: Get not possible, invalid or unknown." in the console, about which I could find virtually nothing:

for(var i=0; i<this.numFields; i++)
{
  var fName = this.getNthFieldName(i);
  var f = this.getField(fName);
 
  if (f.required) {
    app.alert (fName + " is required");
  }
}

If I introduce a typo and test for "f.requiredZZZ" instead of "f.required", it does not crash (and also doesn't work, of course, but it's a step), so would I be correct in guessing that "required" is not what I expected it to be: a boolean flag reflecting the "required" property?

Is there another way to programmatically detect whether a field is required or not? I don't want to enumerate the required fields in code, there will be dozens of different documents to be maintained by non-programmers. It has to detect fields with the "required" checkbox checked in the field properties.

Hope this is a simple problem brought on by my unfamiliarity with the operating environment of Javascript in this context.

Thanks for any tips.