Javascript KVStore Class [TTL]

class KVStore {
  constructor() {
    this.store = {};
    this.timer = setInterval(this.cleanup.bind(this), 1000);
  }

  set(key, value, ttl) {
    this.store[key] = { value: value, ttl: ttl, expiration: Date.now() + ttl };
  }

  get(key) {
    var entry = this.store[key];
    if (entry && entry.expiration > Date.now()) {
      return entry.value;
    }
    return undefined;
  }

  delete(key) {
    delete this.store[key];
  }

  cleanup() {
    var now = Date.now();
    for (var key in this.store) {
      if (this.store[key].expiration <= now) {
        delete this.store[key];
      }
    }
  }
}

var store = new KVStore();

store.set('foo', 'bar', 1000);
console.log(store.get('foo')); // 'bar'

setTimeout(function() {
  console.log(store.get('foo')); // undefined
}, 1100);