Duplicate a task in Javascript for Automation

I’m attempting to duplicate a task using Javascript, but I cannot figure out the location specifier syntax. In Applescript, I would do:

set theDupe to duplicate anItem to after anItem

in Javascript, it should be something like:

var dupe = task.duplicate({to: task.after()});

which gives me the error:

execution error: Error on line 25: Error: Replacement not supported currently, please log a feature request if you need this. (9)

Yeah… I was trying to make a simple project duplicate… dosen’t seems to work…

var of = Application('OmniFocus'),
ofDoc = of.defaultDocument,
projectToDuplicate = ofDoc.flattenedProjects.whose({name: '-= Séance Facturé =-'})[0];
projectToDuplicate.duplicate({to: projectToDuplicate.container()});