how can i listen for a broadcast with js?

[DemonLordDiablo]

i am trying to make a custom block like:
whenbroadcastreceived(message){ //do whatever with "message" }

i can use:
vm.runtime.startHats("event_whenbroadcastreceived", {
BROADCAST_OPTION: data,
})
to send a broadcast, but how can i listen for a broadcast?