LazyExpireMap

LazyExpireMap.js

/**
 * A JavaScript map that lazily expires entries on read
 * @param ttl TTL in seconds
 * @param autoGc Optional garbage collection interval in seconds
 * @example new LazyExpireMap({ ttl : 60, autoGc: 60 })
 */
export class LazyExpireMap extends Map {
  constructor({ ttl, autoGc } = {}) {
    super()

    if (!ttl) {
      throw new Error('Must provide a ttl in seconds')
    }

    if (autoGc) {
      setInterval(() => this.gcAll(), autoGc * 1000)
    }

    this.ttl = ttl
  }

  gcAll() {
    const now = Date.now()
    for (const [key, { timestamp }] of super.entries()) {
      if (timestamp + this.ttl * 1000 < now) {
        super.delete(key)
      }
    }
    return this
  }

  gc(key) {
    const value = super.get(key)
    const now = Date.now()
    if (value && value.timestamp + this.ttl * 1000 < now) {
      super.delete(key)
    }
    return this
  }

  set(key, data) {
    return super.set(key, { data, timestamp: Date.now() })
  }

  get(key) {
    this.gc(key)
    return super.get(key)?.data
  }

  *values() {
    this.gcAll()
    for (const value of super.values()) {
      yield value.data
    }
  }

  has(key) {
    this.gc(key)
    return super.has(key)
  }

  keys() {
    this.gcAll()
    return super.keys()
  }

  *entries() {
    this.gcAll()
    for (const [key, value] of super.entries()) {
      yield [key, value.data]
    }
  }
}