In a future version of Rudder, JavaScript evaluation will be supported in all fields in Directives.
In the meantime, you can already test this functionality out by entering a JavaScript expression in any Directive field, prefixed by "evaljs:". Please be aware that this is unsupported and untested, so do this at your own risk.
If you do encounter any issues, please get in touch or open a ticket - we’d love to hear about them!
There is currently no plan to extend this support to the fields in the Technique editor.