facebook/hermes

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A JavaScript engine optimized for running React Native.

Stars: 11.3k
Forks: 859
Open beginner issues: 0
Indexed issues: 136
Avg merge: 1h 30m
Merged PRs (30d): 3

Dominant language: JavaScript
License: MIT
Last GitHub push: Sep 12, 2026
Latest indexed: Sep 15, 2026
Contributing guide: Contributing guide
Code of conduct: Code of conduct
Beginner labels: No beginner labels indexed

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136 open issues indexed

new Date() not throwing an Invalid Date error Open

bug

facebook/hermes#1148 · 3 comments · 0 reactions · 0 assignees · Indexed Sep 15, 2026
Intl.DateTimeFormat returns incorrect values on real iOS devices Open

bug

facebook/hermes#1172 · 4 comments · 4 reactions · 0 assignees · Indexed Sep 15, 2026
Intl.NumberFormat’s formatToParts not implemented for iOS Open

enhancement Intl

facebook/hermes#1188 · 5 comments · 10 reactions · 0 assignees · Indexed Sep 15, 2026
Hermes seems to take longer to process large promises inside React Native Open

Needs: Triage :mag: Tech: Hermes

facebook/hermes#1573 · 12 comments · 2 reactions · 0 assignees · Indexed Sep 15, 2026
Parser: improve error message when await is used in non-async functions or instead of async Open

enhancement

facebook/hermes#1230 · 0 comments · 5 reactions · 0 assignees · Indexed Sep 15, 2026
Conversion of large array to a Set seems slow Open

enhancement

facebook/hermes#1253 · 5 comments · 0 reactions · 0 assignees · Indexed Sep 15, 2026
'hermes-engine' uses the unencrypted 'http' protocol to transfer the Pod. Open

bug

facebook/hermes#1277 · 0 comments · 0 reactions · 0 assignees · Indexed Sep 15, 2026
Intl.NumberFormat can't always display the number's sign Open

Needs: Triage :mag:

facebook/hermes#1317 · 1 comment · 0 reactions · 0 assignees · Indexed Sep 15, 2026
Intl.NumberFormat with compact notation doesn't display formatting Open

Needs: Triage :mag:

facebook/hermes#1318 · 1 comment · 1 reaction · 0 assignees · Indexed Sep 15, 2026
babel-plugin-syntax-hermes-parser drops chunk names Open

bug

facebook/hermes#1320 · 2 comments · 5 reactions · 1 assignee · Indexed Sep 15, 2026
Using Intl with standalone Hermes app Open

facebook/hermes#1350 · 2 comments · 0 reactions · 0 assignees · Indexed Sep 15, 2026
Support for top level await Open

bug

facebook/hermes#1352 · 1 comment · 8 reactions · 0 assignees · Indexed Sep 15, 2026
[Debugger] Incorrect scope variable information for variable initialized in for-loop Open

bug

facebook/hermes#1355 · 3 comments · 0 reactions · 0 assignees · Indexed Sep 15, 2026
Assertion `IDom && "Reached the top of the tree!"' failed in ./hermes/lib/Optimizer/Scalar/Mem2Reg.cpp Open

bug

facebook/hermes#1357 · 1 comment · 0 reactions · 0 assignees · Indexed Sep 15, 2026
prettier plugin: Infinite loop for malformed graphql relay query Open

bug

facebook/hermes#1359 · 0 comments · 1 reaction · 1 assignee · Indexed Sep 15, 2026
[Profiler] First sample sometimes has timestamp of zero Open

bug

facebook/hermes#1368 · 3 comments · 1 reaction · 0 assignees · Indexed Sep 15, 2026
C++ class bindings Open

enhancement

facebook/hermes#1392 · 3 comments · 0 reactions · 0 assignees · Indexed Sep 15, 2026
Property storage exceeds 196607 properties when sending a file via fetch() Open

need more info

facebook/hermes#1394 · 6 comments · 0 reactions · 0 assignees · Indexed Sep 15, 2026
Feature request: Improved error `async arrow functions are unsupported` Open

enhancement

facebook/hermes#1395 · 5 comments · 0 reactions · 0 assignees · Indexed Sep 15, 2026
Feature Request: Support for Parsing YYYY/MM/DD Date Format in Hermes Engine Open

enhancement

facebook/hermes#1400 · 0 comments · 4 reactions · 0 assignees · Indexed Sep 15, 2026
Intl.NumberFormat does not interpret strings as decimal Open

enhancement

facebook/hermes#1418 · 4 comments · 0 reactions · 0 assignees · Indexed Sep 15, 2026
Unable to get JS function names in HermesSamplingProfiler Open

need more info

facebook/hermes#1414 · 3 comments · 0 reactions · 0 assignees · Indexed Sep 15, 2026
NULL pointer dereference in function getLiveInValue, file lib/Optimizer/Scalar/Mem2Reg.cpp Open

bug

facebook/hermes#1416 · 0 comments · 0 reactions · 0 assignees · Indexed Sep 15, 2026
Bug in scoped function promotion (non-strict mode) Open

bug

facebook/hermes#1455 · 3 comments · 0 reactions · 0 assignees · Indexed Sep 15, 2026
Problems loading emscripten compiled js file in Hermes. Works on JSC/V8. Open

bug

facebook/hermes#1456 · 7 comments · 0 reactions · 0 assignees · Indexed Sep 15, 2026
Intl.PluralRules support Open

enhancement

facebook/hermes#1462 · 0 comments · 13 reactions · 0 assignees · Indexed Sep 15, 2026
Intl.NumberFormat signDisplay option displays odd behaviour Open

Needs: Triage :mag:

facebook/hermes#1466 · 1 comment · 0 reactions · 0 assignees · Indexed Sep 15, 2026
babel-plugin-syntax-hermes-parser fails to parse decorators Open

enhancement

facebook/hermes#1475 · 1 comment · 0 reactions · 0 assignees · Indexed Sep 15, 2026
Missing default rejection tracking and console.log() polyfill to the Hermes CLI Open

need-repro

facebook/hermes#1480 · 13 comments · 0 reactions · 0 assignees · Indexed Sep 15, 2026
top-level await not supported Open

es2022

facebook/hermes#1481 · 4 comments · 0 reactions · 0 assignees · Indexed Sep 15, 2026
toLocaleString date function returns the wrong date for "Asia/Singapore" timezone and 1981 and older years Open

facebook/hermes#1485 · 7 comments · 0 reactions · 0 assignees · Indexed Sep 15, 2026
Property checking in host objects Open

enhancement

facebook/hermes#1490 · 3 comments · 0 reactions · 0 assignees · Indexed Sep 15, 2026
Date getTime unexpected result Open

need-repro

facebook/hermes#1491 · 7 comments · 0 reactions · 0 assignees · Indexed Sep 15, 2026
TypedArrays are not spec-compliant and break Buffer with many ecosystem packages Open

bug

facebook/hermes#1495 · 10 comments · 8 reactions · 0 assignees · Indexed Sep 15, 2026
[Test] Please ignore Open

bug

facebook/hermes#1499 · 1 comment · 0 reactions · 0 assignees · Indexed Sep 15, 2026
Bug: hermes-eslint: no-unused-vars crashes in Flow libdefs with class declarations Open

bug

facebook/hermes#1516 · 0 comments · 3 reactions · 0 assignees · Indexed Sep 15, 2026
new Date('MMM DD, YYYY HH:MM PM') format is not supported Open

enhancement

facebook/hermes#1519 · 11 comments · 0 reactions · 0 assignees · Indexed Sep 15, 2026
prettier plugin: class with generic, extending namespaced base class, fails Open

bug

facebook/hermes#1532 · 0 comments · 0 reactions · 1 assignee · Indexed Sep 15, 2026
On Android pthread_attr_getstack() includes the guard pages in the returned stack size Open

bug

facebook/hermes#1535 · 18 comments · 21 reactions · 0 assignees · Indexed Sep 15, 2026
Intl.DateTimeFormat does not format 2-digit hours correctly Open

bug Intl

facebook/hermes#1537 · 4 comments · 0 reactions · 0 assignees · Indexed Sep 15, 2026
`Intl.RelativeTimeFormat` is unsupported Open

enhancement

facebook/hermes#1539 · 5 comments · 6 reactions · 0 assignees · Indexed Sep 15, 2026
createSnapShotToFile() assertion failure "no active GCScope" Open

bug

facebook/hermes#1542 · 3 comments · 0 reactions · 0 assignees · Indexed Sep 15, 2026
prettier-plugin-hermes-parser: error with prettier when declare namespace Open

bug

facebook/hermes#1546 · 0 comments · 0 reactions · 1 assignee · Indexed Sep 15, 2026
Date.toLocaleString() is off by 2 days for dates before 1582. Open

bug

facebook/hermes#1570 · 1 comment · 0 reactions · 0 assignees · Indexed Sep 15, 2026
Support for ArrayBuffer::isMutableBuffer() and ArrayBuffer::getMutableBuffer() Open

enhancement

facebook/hermes#1578 · 9 comments · 6 reactions · 0 assignees · Indexed Sep 15, 2026
[JSI] Support non-copy `jsi::String` constructors Open

enhancement

facebook/hermes#1597 · 8 comments · 2 reactions · 0 assignees · Indexed Sep 15, 2026
Intl.DateTimeFormat() returns short timeZoneName with GMT offset removed in some locales Open

bug

facebook/hermes#1601 · 4 comments · 2 reactions · 0 assignees · Indexed Sep 15, 2026
TypeError: ownKeys target is non-extensible but key is missing from trap result error when using numeric string keys on Hermes Open

bug

facebook/hermes#1609 · 10 comments · 2 reactions · 0 assignees · Indexed Sep 15, 2026
Adding Node-API support to Static Hermes Open

facebook/hermes#1610 · 0 comments · 0 reactions · 0 assignees · Indexed Sep 15, 2026
Error while building static_h for Windows Open

bug

facebook/hermes#1627 · 7 comments · 0 reactions · 0 assignees · Indexed Sep 15, 2026

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