javascript - Wrapping multiple asynchronous calls into syncronous -

let's have function this

getallepisodes = (show)->    dfrd = new deferred()    eps = []    s of show.seasons       api.getmeallepisodes(s.id).done (episodes)->          eps = eps.concat(episodes)     return dfrd.promise() 

so when should resolve dfrd? can't right after loop, right? makes difficult without knowing exact number of episodes beforehand (without making api calls)