getWithTTL(key) {
		// There are no way to get the ttl of LRU cache :(
		return this.get(key).then(data => {
			return { data, ttl: null };
		});
	}
Get data and ttl from cache by key.

@param {string|Array<string>} key
@returns {Promise}

@memberof MemoryLRUCacher