How to bind to a js property that is a promise (not method)

Oh wait, I think I figured it out. I just moved the properties into the type.

type viewTransition = {
  viewTransitionFinished: promise<unit>,
  viewTransitionReady: promise<unit>,
  viewTransitionUpdateCallbackDone: promise<unit>,
}

@send external skipTransition: (viewTransition, unit) => unit = "skipTransition"

Seems to be working now.