Using string to designate a subform for the instanceManager

Question

var propOptSubformID     = "8011"
var propSubformName     = Concat("SubformPropOption",propOptSubformID,".instanceManager")      //since instanceManager is object
$.resolveNode(propSubformName).setInstances(1)
I get:
I can't seem to find a way to use the instanceManager and successfully reference a subform using a string. Any ideas?
I want to avoid using conditional statements or switch if possible. I have 35 different subforms eachl with 0 instances. I want to identify one of the subforms using a variable (string) and make it exist. There has to be a way to do this, right?
I may have to name all the subforms the same and use an index--but I would like to avoid that, Or, I suppose I could loop through the siblings and compare my string to the subform name--but I think this might end up having the same problem. It would be really good to know how to do it with a string and the instanceManager..
Thanks,
Stephen
PS, I also tried
var propSubformName     = Concat("SubformPropOption",propOptSubformID,".instanceManager.setInstances(1)")
$.resolveNode(propSubformName)
and...  Nothing happens? No error and no subform either?

Answer 1

Thanks Robert,
I might be missing something--I've never seen square brackets used in the way you suggest. Am I missing something?
The subform doesn't have an index[propOptSubformID]  It would have an index[0] when it actually does exist. This isn't really an index problem. That would be easy and I think I may have to go that way (i.e. name them alll the same and reference them by index) if I can't reference the object.instanceManager and use its method setInstances() with a string.
This might be a clue: the error message referred to setInstances() as a property--it is a method(). If it had recognized it as a method, then it the error would have said that the object doesen't have a method setInstances(). Also, it represented the ("1") as a string when it an integer parameter for setInstances().
Stephen