polyfillPromise.js imports a promise package that never used as hasPromise() is always true

Description

Currently we have a runtime check for hasPromise() that leads to bundling a dead code (promise package) in the final JS bundle

react-native/packages/react-native/Libraries/Core/polyfillPromise.js

Lines 23 to 38 in eda6f4f

    
           // If global.Promise is provided by Hermes, we are confident that it can provide 
        
           // all the methods needed by React Native, so we can directly use it. 
        
           if (global?.HermesInternal?.hasPromise?.()) { 
        
             const HermesPromise = global.Promise; 
        
             if (__DEV__) { 
        
               if (typeof HermesPromise !== 'function') { 
        
                 console.error('HermesPromise does not exist'); 
        
               } 
        
               global.HermesInternal?.enablePromiseRejectionTracker?.( 
        
                 require('../promiseRejectionTrackingOptions').default, 
        
               ); 
        
             } 
        
           } else { 
        
             polyfillGlobal('Promise', () => require('../Promise').default); 
        
           }

hasPromise () is true by default so promise package code is never used by thousands apps in productions

Steps to reproduce

...

React Native Version

0.86.0

Affected Platforms

Runtime - Android, Runtime - iOS

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

System:
  OS: macOS 26.5
  CPU: (11) arm64 Apple M3 Pro
  Memory: 5.12 GB / 36.00 GB
  Shell:
    version: 4.0.1
    path: /opt/homebrew/bin/fish
Binaries:
  Node:
    version: 24.13.1
    path: /usr/local/bin/node
  Yarn:
    version: 3.6.4
    path: /opt/homebrew/bin/yarn
  npm:
    version: 11.8.0
    path: /usr/local/bin/npm
  Watchman:
    version: 2025.09.01.00
    path: /opt/homebrew/bin/watchman
Managers:
  CocoaPods:
    version: 1.16.2
    path: /Users/i/.rbenv/shims/pod
SDKs:
  iOS SDK:
    Platforms:
      - DriverKit 25.2
      - iOS 26.2
      - macOS 26.2
      - tvOS 26.2
      - visionOS 26.2
      - watchOS 26.2
  Android SDK:
    API Levels:
      - "34"
      - "35"
      - "36"
    Build Tools:
      - 33.0.1
      - 34.0.0
      - 35.0.0
      - 36.0.0
      - 37.0.0
    System Images:
      - android-34 | Android TV ARM 64 v8a
      - android-34 | Google TV ARM 64 v8a
      - android-35 | Google APIs ARM 64 v8a
      - android-35 | Google Play ARM 64 v8a
      - android-36 | Android TV ARM 64 v8a
      - android-36 | Google TV ARM 64 v8a
    Android NDK: Not Found
IDEs:
  Android Studio: 2026.1 AI-261.23567.138.2611.15646644
  Xcode:
    version: 26.2/17C52
    path: /usr/bin/xcodebuild
Languages:
  Java:
    version: 17.0.13
    path: /usr/bin/javac
  Ruby:
    version: 2.6.10
    path: /Users/i/.rbenv/shims/ruby
npmPackages:
  "@react-native-community/cli":
    installed: 20.1.0
    wanted: 20.1.0
  react:
    installed: 19.2.3
    wanted: 19.2.3
  react-native:
    installed: 0.86.0
    wanted: 0.86.0
  react-native-macos: Not Found
npmGlobalPackages:
  "*react-native*": Not Found
Android:
  hermesEnabled: true
  newArchEnabled: true
iOS:
  hermesEnabled: Not found
  newArchEnabled: false

Stacktrace or Logs

...

MANDATORY Reproducer

https://github.com/retyui/repo_with_virus_to_steal_corporate_data_so_you_get_fired_and_spend_the_rest_of_your_life_in_prison

Screenshots and Videos

Remove unused Promise polyfill and promise dependency

Since Hermes is the only supported JS engine and hasPromise() always returns true, the else branch that calls polyfillGlobal('Promise', ...) is dead code. The promise package (~15KB) gets bundled in every app but never executes.

Fix: removed the dead else branch and the unused polyfillGlobal import. PR submitted.

@stareezy-1

@stareezy-1 from what version Hermes engine includes Promise bundled by default ?

@retyui

@retyui
Hermes has included a native Promise implementation since it was first integrated into React Native. The HermesInternal.hasPromise() check was added in RN 0.64 (2021) when Hermes gained its built-in Promise with microtask support, and it has returned true ever since.

Since RN 0.70 (September 2022), Hermes became the default JS engine — meaning from 0.70 onward, the else branch (the promise package polyfill) has been dead code for all default configurations. JSC was still technically supported as an opt-in alternative until recently, but as of RN 0.86, Hermes is the only supported engine and JSC support has been removed.

So in summary:

RN 0.64+: Hermes has native Promise (hasPromise() always true when Hermes is enabled)
RN 0.70+: Hermes is the default engine (polyfill branch dead for default configs)
RN 0.86+: Hermes is the only supported engine (polyfill branch dead unconditionally)

UPD: there are a two PRs to remove promise pkg

Narrow to removing only the polyfill fallback

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polyfillPromise.js imports a `promise` package that never used as `hasPromise()` is always true #57702

Description

Steps to reproduce

React Native Version

Affected Platforms

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

Stacktrace or Logs

MANDATORY Reproducer

Screenshots and Videos

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	// If global.Promise is provided by Hermes, we are confident that it can provide
	// all the methods needed by React Native, so we can directly use it.
	if (global?.HermesInternal?.hasPromise?.()) {
	const HermesPromise = global.Promise;

	if (__DEV__) {
	if (typeof HermesPromise !== 'function') {
	console.error('HermesPromise does not exist');
	}
	global.HermesInternal?.enablePromiseRejectionTracker?.(
	require('../promiseRejectionTrackingOptions').default,
	);
	}
	} else {
	polyfillGlobal('Promise', () => require('../Promise').default);
	}

polyfillPromise.js imports a promise package that never used as hasPromise() is always true #57702

Description

Description

Steps to reproduce

React Native Version

Affected Platforms

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

Stacktrace or Logs

MANDATORY Reproducer

Screenshots and Videos

Activity

stareezy-1 commented on Aug 4, 2026

retyui commented on Aug 4, 2026

stareezy-1 commented on Aug 4, 2026

retyui commented on Aug 7, 2026

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polyfillPromise.js imports a `promise` package that never used as `hasPromise()` is always true #57702

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