ScopedStorage - Storage API with scope

ScopedStorage.ts

export class ScopedStorage implements Storage {
  [name: string]: any;

  #storage: Storage;
  #prefix: string;

  constructor(storage: Storage, prefix: string) {
    this.#storage = storage;
    this.#prefix = prefix;

    if (prefix === "") {
      throw new Error("ScopedStoage - prefix is empty string, which make the usuage of ScopedStoage unneeded");
    }

    // We don't support `set` or `delete` because it always be buggy, and not really needed in reasonable usuage
    return new Proxy(this, {
      has(target, key) {
        if (typeof key === "string") {
          // Prefix key
          if (target.getItem(prefix + key) != null) return true;

          // If key exist as item it means it's unprefixed key and so we should ignore it
          return target.getItem(key) == null;
        }

        return Reflect.has(target, key);
      },

      get(target, key, receiver) {
        if (typeof key === "string") {
          // Prefix key
          if (target.getItem(prefix + key) != null) return target.getItem(prefix + key);

          // If key exist as item it means it's unprefixed key and so we should ignore it
          if (target.getItem(key) != null) return undefined;
        }

        return Reflect.get(target, key, receiver);
      },

      ownKeys(target) {
        const keys = [];

        for (let key of Reflect.ownKeys(target)) {
          if (typeof key === "string") {
            if (key.startsWith(prefix)) {
              keys.push(key.substring(prefix.length));
              continue;
            }

            // If key exist as item it means it's unprefixed key and so we should ignore it
            if (target.getItem(key) != null) continue;
          }

          keys.push(key);
        }

        return keys;
      },
    });
  }

  get length(): number {
    let count = 0;

    for (let key of Object.keys(this.#storage)) {
      if (key.startsWith(this.#prefix)) count++;
    }

    return count;
  }

  clear(): void {
    let keys = [];

    for (let key of Object.keys(this.#storage)) {
      if (key.startsWith(this.#prefix)) {
        keys.push(key);
      }
    }

    for (let key of keys) {
      this.#storage.removeItem(key);
    }
  }

  getItem(key: string): string | null {
    return this.#storage.getItem(this.#prefix + key);
  }

  key(index: number): string | null {
    let count = 0;

    for (let key of Object.keys(this.#storage)) {
      if (key.startsWith(this.#prefix)) {
        if (count === index) {
          return this.#storage.getItem(key);
        }
        count++;
      }
    }

    return null;
  }

  removeItem(key: string): void {
    this.#storage.removeItem(this.#prefix + key);
  }

  setItem(key: string, value: string): void {
    this.#storage.setItem(this.#prefix + key, value);
  }
}