Communicate microtask queue behavior

[jeromecovington]

It would be great if there were more material documenting the microtask queue and its relationship to/difference from the event loop.

I came across this issue: nodejs/promises#22 but haven't found anything further (at least not linked there).

[mcollina]

To the best of my knowledge, the microtask queue is flushed after each process.nextTick() execution: https://github.com/nodejs/node/blob/cb3d049badb772fc1ea7051540d50c89f73e36dd/lib/internal/process/next_tick.js#L68.

This guide https://nodejs.org/en/docs/guides/event-loop-timers-and-nexttick/ probably needs updating with some info about the microtask queue.

[jeromecovington]

Cool. Yeah that lines up with my understanding that the Promise contract guarantees resolution on the next tick. Presumably microtasks are flushed without any priority other than queue order.

Will attempt to dig in here, if I come up with enough material I'll see about adding to the docs.