rudeshark.net/packages/client/src/scripts/idb-proxy.ts

// FirefoxのプライベートモードなどではindexedDBが使用不可能なので、
// indexedDBが使えない環境ではlocalStorageを使う
import {
	get as iget,
	set as iset,
	del as idel,
} from 'idb-keyval';

const fallbackName = (key: string) => `idbfallback::${key}`;

let idbAvailable = typeof window !== 'undefined' ? !!window.indexedDB : true;

if (idbAvailable) {
	iset('idb-test', 'test').catch(err => {
		console.error('idb error', err);
		console.error('indexedDB is unavailable. It will use localStorage.');
		idbAvailable = false;
	});
} else {
	console.error('indexedDB is unavailable. It will use localStorage.');
}

export async function get(key: string) {
	if (idbAvailable) return iget(key);
	return JSON.parse(localStorage.getItem(fallbackName(key)));
}

export async function set(key: string, val: any) {
	if (idbAvailable) return iset(key, val);
	return localStorage.setItem(fallbackName(key), JSON.stringify(val));
}

export async function del(key: string) {
	if (idbAvailable) return idel(key);
	return localStorage.removeItem(fallbackName(key));
}