Promise rejection in timeout (versus module-level) treated as unhandled by debugger

Version

v22.4.0

Platform

Darwin Hypothesis.local 24.0.0 Darwin Kernel Version 24.0.0: Thu Jun 20 20:36:19 PDT 2024; root:xnu-11215.0.115.501.3~1/RELEASE_ARM64_T8103 arm64

Subsystem

No response

What steps will reproduce the bug?

Create this script:

setTimeout(() => {
  Promise.reject().catch(() => { })
}, 1)

And run it in the debugger with break on Uncaught enabled.

How often does it reproduce? Is there a required condition?

Every time. Note this does not happen if Promise.reject() is at top level instead of wrapped in setTimeout().

What is the expected behavior? Why is that the expected behavior?

It is expected that the debugger does (1) not pause on such a promise or (2) only pauses on such a promise if breakOnException is enabled.

The HTML spec guarantees that promise rejections are not considered unhandled if a handler is then synchronously attached.

What do you see instead?

Node breaks synchronously on the creation of the rejected promise. Similar issues happen when using the VSCode debugger and Chrome debugger.

node inspect promisetest.js
< Debugger listening on ws://127.0.0.1:9229/d18cff1f-6886-4ff6-9a4f-404128bd150a
< For help, see: https://nodejs.org/en/docs/inspector
< 
< Debugger attached.
< 
 ok
Break on start in promisetest.js:1
> 1 setTimeout(() => {
  2   Promise.reject().catch(() => { })
  3 }, 1)
debug> breakOnUncaught
debug> c
promiseRejection in promisetest.js:2
  1 setTimeout(() => {
> 2   Promise.reject().catch(() => { })
  3 }, 1)
  4 

Additional information

A downstream issue where this interferes with usage of the web streams API: #51093

I too have been incredibly confused by this, as it makes it seem like even correct usage of promises is developer error.

VSCode reports this as "Exception has occurred" instead of "promiseRejection".

首先运行提供的脚本，使用 node inspect、breakOnUncaught 并附加调试器，然后将 timeout 包装的 rejection 与顶层情况进行比较。跟踪在同步附加处理程序时，setTimeout 内创建的 promise rejection 是如何报告的；当调试器不会因该已处理的 rejection 而暂停时完成，除非启用了 breakOnException。