hardcoded 2 second delay before `onUnhandled` fires

[marcospgp]

Description

Problem

React Native's unhandled promise rejection handler has a hardcoded 2-second delay before onUnhandled fires. This causes a significant UX problem: users wait 2 seconds before seeing any error feedback.

Root Cause

This is not a Hermes issue - it's in the promise npm package that React Native uses for rejection tracking.

From promise/src/rejection-tracking.js:

setTimeout(
  onUnhandled.bind(null, promise._rejectionId),
  matchWhitelist(err, DEFAULT_WHITELIST) ? 100 : 2000
)

• 100ms for ReferenceError, TypeError, RangeError (programmer bugs)
• 2000ms for everything else (to allow late .catch() attachments)

From the npm docs:

"To reduce the chance of false-positives there is a delay of up to 2 seconds before errors are logged."

Impact

Most app errors (network failures, API errors, business logic) get the 2-second delay, not the 100ms path. This makes error handling feel sluggish.

Suggested Improvement

Consider:

1. Making the delay configurable via options
2. Reducing the default delay (2s feels excessive in 2025)
3. Documenting this behavior prominently (it's buried in the npm readme)

Workaround

Intercept errors before they become "unhandled rejections." For example, tRPC's MutationCache.onError or similar framework-level hooks fire immediately.

References

• Source code: https://github.com/then/promise/blob/master/src/rejection-tracking.js
• npm package: https://www.npmjs.com/package/promise

Steps to reproduce

see above

React Native Version

latest

Affected Platforms

Runtime - iOS

Output of npx @react-native-community/cli info

n/a

Stacktrace or Logs

n/a

MANDATORY Reproducer

n/a

Screenshots and Videos

No response

[react-native-bot]

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[react-native-bot]

Warning

Could not parse version: We could not find or parse the version number of React Native in your issue report. Please use the template, and report your version including major, minor, and patch numbers - e.g. 0.76.2.

[react-native-bot]

Warning

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[react-native-bot]

This issue is waiting for author's feedback since 24 days. Please provide the requested feedback or this will be closed in 7 days.

[marcospgp]

this issue is self explanatory

[react-native-bot]

This issue is stale because it has been open for 180 days with no activity. It will be closed in 7 days unless you comment on it or remove the "Stale" label.