Description
Description
On iOS and Android (not web), calling StyleSheet.flatten with null/undefined/false returns undefined.
The TypeScript signature of flatten is flatten<T>(style?: StyleProp<T>): T. null/undefined/false are valid StyleProps, so passing them to flatten should be valid, but flatten is supposed to return T (some style object), and undefined is usually not a valid T.
Widening the return type of flatten to T | undefined is an option, but would be a public API change. I think changing the function to return {} for falsy values is more correct, since you probably want to get a final computed, flattened style object, and don't care what the input was or if it was falsy.
Steps to reproduce
On iOS or Android:
console.log(typeof StyleSheet.flatten(false)) // => 'undefined'
React Native Version
0.75.2
Affected Platforms
Runtime - Android, Runtime - iOS
Output of npx react-native info
System:
OS: macOS 14.2
CPU: (8) arm64 Apple M2
Memory: 339.17 MB / 8.00 GB
Shell:
version: "5.9"
path: /bin/zsh
Binaries:
Node:
version: 22.3.0
path: ~/.volta/tools/image/node/22.3.0/bin/node
Yarn:
version: 3.6.4
path: ~/.volta/tools/image/yarn/4.3.1/bin/yarn
npm:
version: 10.8.1
path: ~/.volta/tools/image/node/22.3.0/bin/npm
Watchman:
version: 2024.07.01.00
path: /opt/homebrew/bin/watchman
Managers:
CocoaPods:
version: 1.15.2
path: /Users/hazel/.rbenv/shims/pod
SDKs:
iOS SDK:
Platforms:
- DriverKit 23.5
- iOS 17.5
- macOS 14.5
- tvOS 17.5
- visionOS 1.2
- watchOS 10.5
Android SDK: Not Found
IDEs:
Android Studio: Not Found
Xcode:
version: 15.4/15F31d
path: /usr/bin/xcodebuild
Languages:
Java: Not Found
Ruby:
version: 2.7.4
path: /Users/hazel/.rbenv/shims/ruby
npmPackages:
"@react-native-community/cli": Not Found
react:
installed: 18.3.1
wanted: 18.3.1
react-native:
installed: 0.75.2
wanted: 0.75.2
react-native-macos: Not Found
npmGlobalPackages:
"*react-native*": Not Found
Android:
hermesEnabled: true
newArchEnabled: false
iOS:
hermesEnabled: true
newArchEnabled: fals
Stacktrace or Logs
N/A
Reproducer
https://snack.expo.dev/@catboyfan/stylesheet-flatten-undefined
Screenshots and Videos
No response