interest-map.js

async function getInterestMap() {
  	// the cache key is interests concatenated with a v and the latest application version number
	const cacheKey = `interests:v${packageInfo.version.replace(/\./g, ':')}`;
  
  	// this portion of the code get the cached data using the cache key
	let str = await cache.get(cacheKey);
  	// and this parses the JSON string into an object
	let interestMap = JSON.parse(str);
  
  	// in the event that our cache has expired or is new, we add it back to Redis or refresh the cache
	if (!interestMap) {
		// we'll populate this in a bit
		interestMap = {};
		
		// select featured rss and podcasts synchronously
		const rss = await RSS.findFeatured();
		const podcast = await Podcast.findFeatured();
		
		// loop over the concatenated array
		for (let p of [...rss, ...podcast]) {
			let k = p.interest || 'featured'; // if it doesn't have an iterest, make it featured
			let d = p.toObject(); // convert the mongoose object to a plain javascript object
			d.type = p.constructor.modelName == 'RSS' ? 'rss' : 'podcast'; // some mongoose required magic
	
			if (!(k in interestMap)) {
				interestMap[k] = [];
			}
			
			// push the key and value into the interestMap array
			interestMap[k].push(d);
		}
		
		// set the cache
		let cached = await cache.set(
			cacheKey, // generated cache key for uniqeness
			JSON.stringify(interestMap), // interest object as JSON
			'EX', // expiration command
			60 * 30, // expiration
		);
	}

	return interestMap;
}

// called in the user signup method (not shown)
const interests = await interestMap();