Lesson 25 — Ultimate: KV store with TTL

Boss level: a mini Redis

Redis is a popular in-memory key-value store: you set a value under a key and get it back very fast. Memory is limited, so when the store is full it evicts (removes) an old key. A JavaScript Map remembers insertion order, so m.keys().next().value is the oldest key.

const oldest = m.keys().next().value;
m.delete(oldest);

Note: this playground runs JavaScript in your browser, not in real Node, so Node-only tools (like fs or http) are not available. The exercise is a small plain-JS simulation of the Node idea.

Why it matters: caching layers like this sit in front of almost every busy backend.