Commit 8e978bd
doc: clarify cjs/esm diff in queueMicrotask() vs process.nextTick()
the section comparing `queueMicrotask()` and `process.nextTick()`
doesn't address the different scheduling behavior that the two
functions have in cjs and esm modules, the section's introductory mjs
example also provides an incorrect output, the changes here address
such by explaining the difference between the two module types and
updating the example accordingly
PR-URL: #56659
Fixes: #45048
Reviewed-By: Yagiz Nizipli <yagiz@nizipli.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>1 parent ae360c3 commit 8e978bd
1 file changed
Lines changed: 22 additions & 16 deletions
| Original file line number | Diff line number | Diff line change | |
|---|---|---|---|
@@ -2993,34 +2993,40 @@ function definitelyAsync(arg, cb) { | |||
| 2993 | 2993 | ||
| 2994 | 2994 | ### When to use `queueMicrotask()` vs. `process.nextTick()` | |
| 2995 | 2995 | ||
| 2996 | - The [`queueMicrotask()`][] API is an alternative to `process.nextTick()` that | ||
| 2997 | - also defers execution of a function using the same microtask queue used to | ||
| 2998 | - execute the then, catch, and finally handlers of resolved promises. Within | ||
| 2999 | - Node.js, every time the "next tick queue" is drained, the microtask queue | ||
| 2996 | + The [`queueMicrotask()`][] API is an alternative to `process.nextTick()` that instead of using the | ||
| 2997 | + "next tick queue" defers execution of a function using the same microtask queue used to execute the | ||
| 2998 | + then, catch, and finally handlers of resolved promises. | ||
| 2999 | + | ||
| 3000 | + Within Node.js, every time the "next tick queue" is drained, the microtask queue | ||
| 3000 | 3001 | is drained immediately after. | |
| 3001 | 3002 | ||
| 3003 | + So in CJS modules `process.nextTick()` callbacks are always run before `queueMicrotask()` ones. | ||
| 3004 | + However since ESM modules are processed already as part of the microtask queue, there | ||
| 3005 | + `queueMicrotask()` callbacks are always exectued before `process.nextTick()` ones since Node.js | ||
| 3006 | + is already in the process of draining the microtask queue. | ||
| 3007 | + | ||
| 3002 | 3008 | ```mjs | |
| 3003 | 3009 | import { nextTick } from 'node:process'; | |
| 3004 | 3010 | ||
| 3005 | - Promise.resolve().then(() => console.log(2)); | ||
| 3006 | - queueMicrotask(() => console.log(3)); | ||
| 3007 | - nextTick(() => console.log(1)); | ||
| 3011 | + Promise.resolve().then(() => console.log('resolve')); | ||
| 3012 | + queueMicrotask(() => console.log('microtask')); | ||
| 3013 | + nextTick(() => console.log('nextTick')); | ||
| 3008 | 3014 | // Output: | |
| 3009 | - // 1 | ||
| 3010 | - // 2 | ||
| 3011 | - // 3 | ||
| 3015 | + // resolve | ||
| 3016 | + // microtask | ||
| 3017 | + // nextTick | ||
| 3012 | 3018 | ``` | |
| 3013 | 3019 | ||
| 3014 | 3020 | ```cjs | |
| 3015 | 3021 | const { nextTick } = require('node:process'); | |
| 3016 | 3022 | ||
| 3017 | - Promise.resolve().then(() => console.log(2)); | ||
| 3018 | - queueMicrotask(() => console.log(3)); | ||
| 3019 | - nextTick(() => console.log(1)); | ||
| 3023 | + Promise.resolve().then(() => console.log('resolve')); | ||
| 3024 | + queueMicrotask(() => console.log('microtask')); | ||
| 3025 | + nextTick(() => console.log('nextTick')); | ||
| 3020 | 3026 | // Output: | |
| 3021 | - // 1 | ||
| 3022 | - // 2 | ||
| 3023 | - // 3 | ||
| 3027 | + // nextTick | ||
| 3028 | + // resolve | ||
| 3029 | + // microtask | ||
| 3024 | 3030 | ``` | |
| 3025 | 3031 | ||
| 3026 | 3032 | For _most_ userland use cases, the `queueMicrotask()` API provides a portable | |
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