This is a general decorator function that caches the return value of a function for a specified amount of time inside of a redis database.

redis-cached.ts

import type { Redis } from "ioredis";

/**
 * This is a general decorator function that caches the
 * return value of a function for a specified amount of time
 * inside of a redis database. This can be used
 * to save responses from API requests, for example.
 * Caveat: This function is not typesafe, since we don't know
 * which type of data is saved in the redis database.
 * @param fun any function (without arguments)
 * @param duration caching duration in seconds
 * @returns the function return value when the cache is empty or expired, or the cached value
 */
export function redis_cached<T>(
	redis: Redis,
	key: string,
	fun: () => Promise<T>,
	duration: number,
) {
	return async function (): Promise<T> {
		const cached_value = await redis.get(key);
		if (cached_value) {
			return JSON.parse(cached_value);
		}
		const result = await fun();
		save_in_redis();
		return result;

		async function save_in_redis() {
			await redis.set(key, JSON.stringify(result), "EX", duration);
		}
	};
}