Callbacks themselves represent an inversion of control. So inverting the callback pattern is actually an inversion of inversion, or an uninversion of control -- restoring control back to the calling code where we wanted it to be in the first place.
если не передать в промис
fulfillment handler или rejection handler, то подставятся обработчики по умолчанию:function(v) {
return v;
}
function(err) {
throw err;
}