Promise.resolve().then vs setImmediate vs nextTick

Question

NodeJS 0.11 as well as io.js and the Node 0.12 branch all ship with native promises.

Native promises have a .then method which always executes on a future event loop

Answer 1

Using Promise.resolve().then has no advantages over nextTick. It runs on the same queue, but have slightly higher priority, that is, promise handler can prevent next tick callback from ever running, the opposite is not possible. This behaviour is an implementation detail and should not be relied on.

Promise.resolve().then is obviously slower (a lot, I think), because it creates two promises which will be thrown away.

You can find extensive implementation info here: https://github.com/joyent/node/pull/8325

The most important part: Promise.resolve().then is like nextTick and not like setImmediate. Using it n place of setImmediate can change your code behaviour drastically.