allowFontScaling = false not working on react native 0.78.1

[Ahmed-Bilal-01]

Description

I have developed an app and currently working on it iOS side. By increasing the font size from mobile's setting disturbs all the UI of the app even have applied allowFontScaling = false globally from index.js.

With normal scaling:

With increasing font scale:

my index.js:

import { Text,TextInput, AppRegistry } from "react-native";
import App from "./App";
import { name as appName } from "./app.json";

Text.defaultProps = Text.defaultProps || {};
TextInput.defaultProps = TextInput.defaultProps || {};
Text.defaultProps.allowFontScaling = false;
TextInput.defaultProps.allowFontScaling = false;

AppRegistry.registerComponent(appName, () => App);

Steps to reproduce

1. yarn install
2. cd ios
3. pod install
4. cd ..
5. yarn ios

React Native Version

0.78.1

Affected Platforms

Build - MacOS

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

System:
  OS: macOS 14.6
  CPU: (12) x64 Intel(R) Core(TM) i7-9750H CPU @ 2.60GHz
  Memory: 86.38 MB / 16.00 GB
  Shell:
    version: "5.9"
    path: /bin/zsh
Binaries:
  Node:
    version: 22.15.0
    path: /usr/local/bin/node
  Yarn:
    version: 1.22.22
    path: /usr/local/bin/yarn
  npm:
    version: 10.9.2
    path: /usr/local/bin/npm
  Watchman:
    version: 2025.04.28.00
    path: /usr/local/bin/watchman
Managers:
  CocoaPods:
    version: 1.16.2
    path: /usr/local/bin/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: 2024.3 AI-243.24978.46.2431.13363775
  Xcode:
    version: 15.4/15F31d
    path: /usr/bin/xcodebuild
Languages:
  Java:
    version: 17.0.15
    path: /usr/bin/javac
  Ruby:
    version: 2.6.10
    path: /usr/bin/ruby
npmPackages:
  "@react-native-community/cli":
    installed: 15.0.1
    wanted: 15.0.1
  react:
    installed: 19.0.0
    wanted: 19.0.0
  react-native:
    installed: 0.78.1
    wanted: 0.78.1
  react-native-macos: Not Found
npmGlobalPackages:
  "*react-native*": Not Found
Android:
  hermesEnabled: false
  newArchEnabled: false
iOS:
  hermesEnabled: true
  newArchEnabled: true

Stacktrace or Logs

Provided in description

MANDATORY Reproducer

Can be checked by any demo react native 0.78.1 app
https://snack.expo.dev/tyWyGOMwYeNYJH8VuBoJ_

Screenshots and Videos

With normal scaling:

With increasing font scale:

[react-native-bot]

Tip

Newer version available: You are on a supported minor version, but it looks like there's a newer patch available - 0.78.2. Please upgrade to the highest patch for your minor or latest and verify if the issue persists (alternatively, create a new project and repro the issue in it). If it does not repro, please let us know so we can close out this issue. This helps us ensure we are looking at issues that still exist in the most recent releases.

[react-native-bot]

Warning

Missing reproducer: We could not detect a reproducible example in your issue report. Reproducers are mandatory and we can accept only one of those as a valid reproducer:

• For majority of bugs: send us a Pull Request with the RNTesterPlayground.js edited to reproduce your bug.
• If your bug is UI related: a Snack
• If your bug is build/upgrade related: a project using our Reproducer Template

You can read more about about it on our website: How to report a bug.

[react-native-bot]

Tip

Newer version available: You are on a supported minor version, but it looks like there's a newer patch available - undefined. Please upgrade to the highest patch for your minor or latest and verify if the issue persists (alternatively, create a new project and repro the issue in it). If it does not repro, please let us know so we can close out this issue. This helps us ensure we are looking at issues that still exist in the most recent releases.

[cipolleschi]

I tested locally with a small playground and it looks like it is working:

function Playground() {
  return (
    <View style={styles.container}>
      <Text>This text should scale</Text>
      <Text allowFontScaling={false}>This text should NOT scale</Text>
    </View>
  );
}

I wonder whether it might be the default text props that are not working fine....

Yep, it looks like that the defaultProps are not working. I'll investigate internally why is that and we will come back with a fix.

[Ahmed-Bilal-01]

Yes, the issue is related to defaultProps specifically and not able to applyallowFontScale = false globally. It works fine in implementing on individual Text fields.

This issue persist in react-native 0.79 as well. I guess it came after 0.77 update.

[cipolleschi]

I dug a bit more into the issue. The problem is that defaultProps are not supported anymore for function components by React itself, not React Native: source.

This is the React 19 upgrade guide, so it is likely that this stopped working in 0.78 when we ship React 19.

You should migrate your app away from that pattern, as it is not supported anymore.

A simple way to do it would be to create your own text component:

function Text(props) {

  return <Text allowFontScaling={false} ...props />
} 

And replace all the import { ..., Text, ...} from 'react-native' with import Text from './path/to/your/text/compononent'.

[pedrogarciyalopez]

I'm not sure how good this solution is, but it allows disabling font scaling globally in React Native 0.79. Guys, what do you think about this?

import { Text, TextInput } from 'react-native';

const originalTextRender = Text.render;

const originalTextInputRender = TextInput.render;

Text.render = function (...args) {
  const origin = originalTextRender.apply(this, args);

  return React.cloneElement(origin, {
    allowFontScaling: false,
  });
};

TextInput.render = function (...args) {
  const origin = originalTextInputRender.apply(this, args);

  return React.cloneElement(origin, {
    allowFontScaling: false,
  });
};