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 cycle.
So far I've been using setImmediate
to queue things to the next iteration of the event loop ever since I switched from nextTick:
setImmediate(deferThisToNextTick); // My NodeJS 0.10 code process.nextTick(deferThisToNextTick); // My NodeJS 0.8 code
Since we now have a new way to do this:
Promise.resolve().then(deferThisToNextTick);
Which should I use? Also - does Promise.resolve.then
act like setImmediate
or like nextTick
with regards to code running before or after the event loop?
process. nextTick() is used to schedule a callback function to be invoked in the next iteration of the Event Loop. setImmediate() method is used to execute a function right after the current event loop finishes.
resolve() The Promise. resolve() method "resolves" a given value to a Promise . If the value is a promise, that promise is returned; if the value is a thenable, Promise. resolve() will call the then() method with two callbacks it prepared; otherwise the returned promise will be fulfilled with the value.
Use nextTick() when you want to make sure that in the next event loop iteration that code is already executed.
setImmediate() vs setTimeout()setImmediate() is designed to execute a script once the current poll phase completes. setTimeout() schedules a script to be run after a minimum threshold in ms has elapsed.
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.
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