The problem with "var d = defer(); ...; return d.promise;" vs "return new Promise((resolve, reject) => {...});" is that the former does not protect you from s

The problem with "var d = defer(); ...; return d.promise;" vs "return new Promise((resolve, reject) => {...});" is that the former does not protect you from synchronous throws. In the latter (at least with every promise library and native promise implementation I've seen) if the code in '...' throws, it rejects the promise with the thrown error. In the former, it throws synchronously, which especially in node is almost never what you want. Besides, if you need to promisify a node-like function you should just use Bluebird's promisification features; no point in doing it yourself. The fact that Bluebird is also the most debuggable and performant Promise implementation (including native) is just icing on the cake.