cra-template-rb/template/src/styles/theme/utils.ts

The official React Boilerplate template for Create React App

import { ThemeKeyType } from './slice/types';

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export const isSystemDark = window?.matchMedia
  ? window.matchMedia('(prefers-color-scheme: dark)')?.matches
  : undefined;

export function saveTheme(theme: ThemeKeyType) {
  window.localStorage && localStorage.setItem('selectedTheme', theme);
}

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export function getThemeFromStorage(): ThemeKeyType | null {
  return window.localStorage
    ? (localStorage.getItem('selectedTheme') as ThemeKeyType) || null
    : null;
}