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));
}