From ee6c467c8a7b451b4d785f0068f4e130de48ecc1 Mon Sep 17 00:00:00 2001
From: James M Snell <jasnell@gmail.com>
Date: Mon, 22 Feb 2021 15:03:09 -0800
Subject: [PATCH] doc: recommend queueMicrotask over process.nextTick

We likely cannot ever deprecate process.nextTick, but we can start
steering people towards queueMicrotask for most cases.

Signed-off-by: James M Snell <jasnell@gmail.com>
Fixes: https://github.com/nodejs/node/issues/36870

PR-URL: https://github.com/nodejs/node/pull/37484
Reviewed-By: Gus Caplan <me@gus.host>
Reviewed-By: Robert Nagy <ronagy@icloud.com>
---
 doc/api/process.md | 65 ++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 65 insertions(+)

diff --git a/doc/api/process.md b/doc/api/process.md
index 5e798af0bb6cc4..938f348b21959b 100644
--- a/doc/api/process.md
+++ b/doc/api/process.md
@@ -1730,6 +1730,70 @@ function definitelyAsync(arg, cb) {
 }
 ```
 
+### When to use `queueMicrotask()` vs. `process.nextTick()`
+
+The [`queueMicrotask()`][] API is an alternative to `process.nextTick()` that
+also defers execution of a function using the same microtask queue used to
+execute the then, catch, and finally handlers of resolved promises. Within
+Node.js, every time the "next tick queue" is drained, the microtask queue
+is drained immediately after.
+
+```js
+Promise.resolve().then(() => console.log(2));
+queueMicrotask(() => console.log(3));
+process.nextTick(() => console.log(1));
+// Output:
+// 1
+// 2
+// 3
+```
+
+For *most* userland use cases, the `queueMicrotask()` API provides a portable
+and reliable mechanism for deferring execution that works across multiple
+JavaScript platform environments and should be favored over `process.nextTick()`.
+In simple scenarios, `queueMicrotask()` can be a drop-in replacement for
+`process.nextTick()`.
+
+```js
+console.log('start');
+queueMicrotask(() => {
+  console.log('microtask callback');
+});
+console.log('scheduled');
+// Output:
+// start
+// scheduled
+// microtask callback
+```
+
+One note-worthy difference between the two APIs is that `process.nextTick()`
+allows specifying additional values that will be passed as arguments to the
+deferred function when it is called. Achieving the same result with
+`queueMicrotask()` requires using either a closure or a bound function:
+
+```js
+function deferred(a, b) {
+  console.log('microtask', a + b);
+}
+
+console.log('start');
+queueMicrotask(deferred.bind(undefined, 1, 2));
+console.log('scheduled');
+// Output:
+// start
+// scheduled
+// microtask 3
+```
+
+There are minor differences in the way errors raised from within the next tick
+queue and microtask queue are handled. Errors thrown within a queued microtask
+callback should be handled within the queued callback when possible. If they are
+not, the `process.on('uncaughtException')` event handler can be used to capture
+and handle the errors.
+
+When in doubt, unless the specific capabilities of `process.nextTick()` are
+needed, use `queueMicrotask()`.
+
 ## `process.noDeprecation`
 <!-- YAML
 added: v0.8.0
@@ -2720,6 +2784,7 @@ cases:
 [`process.kill()`]: #process_process_kill_pid_signal
 [`process.setUncaughtExceptionCaptureCallback()`]: process.md#process_process_setuncaughtexceptioncapturecallback_fn
 [`promise.catch()`]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Promise/catch
+[`queueMicrotask()`]: globals.md#globals_queuemicrotask_callback
 [`readable.read()`]: stream.md#stream_readable_read_size
 [`require()`]: globals.md#globals_require
 [`require.main`]: modules.md#modules_accessing_the_main_module