Map으로 localStorage 래핑 — JSON.stringify(map) 은 {} 라서 [...map](엔트리 배열)으로 저장하고 new Map(entries) 로 되살린다¹

class LocalStorageMap {
  constructor(storageKey) {
    this.storageKey = storageKey
    this.map = this.loadFromStorage()
  }

  loadFromStorage() {
    const data = localStorage.getItem(this.storageKey)
    return data ? new Map(JSON.parse(data)) : new Map()
  }

  saveToStorage() {
    localStorage.setItem(this.storageKey, JSON.stringify([...this.map]))
  }

  set(key, value) {
    this.map.set(key, value)
    this.saveToStorage()
  }

  get(key) {
    return this.map.get(key)
  }

  delete(key) {
    const result = this.map.delete(key)
    this.saveToStorage()
    return result
  }

  clear() {
    this.map.clear()
    localStorage.removeItem(this.storageKey)
  }
}

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Footnotes

1. JSON.stringify() - MDN: “Only enumerable own properties are visited. This means Map, Set, etc. will become “{}”.“ ↩

2. Storage quotas and eviction criteria - MDN: “Browsers can store up to 5 MiB of local storage, and 5 MiB of session storage per origin.” · “Once this limit is reached, browsers throw a QuotaExceededError exception” ↩