intermediate

TTL cache mechanics

Complete the lazy-expiry path of a TTL cache — the write that stamps an expiry and the read that honours it.

interface Entry {
  value: string
  expiresAt: number
}

export class TTLCache {
  #store = new ___<string, Entry>()
  #ttlMs: number

  constructor(ttlMs: number) {
    this.#ttlMs = ttlMs
  }

  set(key: string, value: string): void {
    this.#store.set(key, {
      value,
      expiresAt: Date.___() + this.#ttlMs,
    })
  }

  get(key: string): string | undefined {
    const entry = this.#store.get(key)
    if (entry === undefined) return undefined
    if (Date.now() > entry._________) {
      this.#store.______(key)
      return undefined
    }
    return entry.value
  }
}

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