react native - get font scale

getFontScale.ts

import {PixelRatio, Platform} from 'react-native';

type fontScales = -3 | -2 | -1 | 0 | 1 | 2 | 3;

type iOS_fontScales = '0.823' | '0.882' | '0.941' | '1' | '1.118' | '1.235' | '1.353';
type iOS_fontScalesMap<T> = {[scale in iOS_fontScales]: T};
const fontScale_iOS: iOS_fontScalesMap<number> = {
  '0.823': -3,
  '0.882': -2,
  '0.941': -1,
  '1': 0,
  '1.118': 1,
  '1.235': 2,
  '1.353': 3,
};

type android_fontScales = '0.8500000238418579' | '1' | '1.149999976158142' | '1.2999999523162842';
type android_fontScalesMap<T> = {[scale in android_fontScales]: T};
const fontScale_android: android_fontScalesMap<number> = {
  '0.8500000238418579': -1,
  '1': 0,
  '1.149999976158142': 1,
  '1.2999999523162842': 2,
};

export const getFontScaleUtil = (): fontScales => {
  const fontScaleFromPixelRatio = PixelRatio.getFontScale();

  return Platform.select({
    ios: fontScale_iOS[String(fontScaleFromPixelRatio) as iOS_fontScales],
    android: fontScale_android[String(fontScaleFromPixelRatio) as android_fontScales],
    default: 0,
  }) as fontScales;
};

export default getFontScaleUtil;