Also, fun is that `.nodeify(cb)` protects against undefined. So, it's a handy way to make your library support both promises and callbacks. module.exports

Also, fun is that `.nodeify(cb)` protects against undefined. So, it's a handy way to make your library support both promises and callbacks. module.exports = function (arg, optionalCb) { return promiseReturningFn(arg).nodeify(optionalCb); };