A drop-in replacement for the JS `fetch` method which caches all GET requests. Supports an additional parameter `cachePeriod` allowing you to specify how recent should the response be.

cachedFetch.ts

const maxCachePeriod = 3000;
const cache = new Map();
setInterval(() => {
    const now = +new Date();
    cache.forEach((value, key, map) => {
        if (now - value.time > maxCachePeriod) {
            cache.delete(key);
        }
    });
}, maxCachePeriod);

const cachedFetch(url: string, config: HttpReqConfig, cachePeriod: number = maxCachePeriod): Promise<Response> {
    if (config.method === 'get') {
        const cacheResponse = cache.get(url);
        if (cacheResponse !== undefined && +new Date() - cacheResponse.time < cachePeriod) {
            // console.log('Returning from front-end cache ', url, ' from ', +new Date() - cacheResponse.time, ' millis ago');
            return cacheResponse.response.then((response: Response) => response.clone());
        } else {
            const response = fetch(url, config);
            cache.set(url, {
                time: +new Date(),
                response
            });
            return response.then((response) => response.clone());
        }
    } else {
        return fetch(url, config);
    }
}