In memory caching to reduce data usage for frequent API requests, repeated data processing or similar use cases.

createCache.ts

const FIVE_MINUTES = 1000 * 60 * 5
function createCache<K, V>({ maxAge }: { maxAge: number }) {
    const cache = new Map<
        K,
        V & { cachedAt: ReturnType<(typeof Date)['now']> }
    >()

    return {
        set(key: K, value: V) {
            cache.set(key, { ...value, cachedAt: Date.now() })
        },

        /**
         * Verify that the value both exists and that it's newer than `maxAge`
         */
        has(key: K) {
            const value = cache.get(key)
            if (value && Date.now() - value.cachedAt < maxAge) {
                return true
            }

            return false
        },

        get(key: K) {
            const value = cache.get(key)
            if (value) {
                // Make a copy with the actual data and delete internal caching details
                const dataOnly: V = { ...value }
                delete (dataOnly as V & { cachedAt?: number }).cachedAt
                return dataOnly
            }
        },
    }
}

const cachedCases = createCache<Case['beteckning'], Case>({
    maxAge: FIVE_MINUTES,
})