const fetchDocument = pMemoize(async (url: string): Promise<string> => {
	const request = await fetch(url, {
		headers: {
			Accept: 'text/html',
		},
	});
	return request.text();
}, {
	cache: {
		async get(url: string): Promise<string | undefined> {
			try {
				return await readFile(`./test/.cache/${filenamify(url)}.html`, 'utf8');
			} catch {
				return undefined;
			}
		},
		async set(url: string, contents: string): Promise<void> {
			await writeFile(`./test/.cache/${filenamify(url)}.html`, contents);
		},
		async has(url: string): Promise<boolean> {
			return Boolean(await this.get(url));
		}
	}
});

Type '(url: string) => Promise<string | undefined>' is not assignable to type '(key: unknown) => string | Promise<string | undefined> | undefined'.
  Types of parameters 'url' and 'key' are incompatible.
    Type 'unknown' is not assignable to type 'string'.ts(2322)