Wrap a web storage with a prefix

wrapped-storage.ts

/**
 * Wrap a web storage with a prefix.
 * @author Michael Fedora
 * @link https://gist.github.com/MichaelFedora/031e1ec7a3df736b2b004d6b437e526e
 */
export class WrappedStorage implements Storage {
  #store: Storage;
  #prefix: string;

  #key(k: string): string { return `${this.#prefix}_${k}`; }
  #keys(): string[] {
    const keys = new Set<string>();
    for(let i = 0; i < this.#store.length; i++)
      if(this.#store.key(i)?.startsWith(`${this.#prefix}_`))
        keys.add(this.#store.key(i)!);

    return Array.from(keys);
  }

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

  getItem(key: string): string | null {
    return this.#store.getItem(this.#key(key));
  }

  setItem(key: string, value: string): void {
    this.#store.setItem(this.#key(key), value);
  }

  removeItem(key: string): void {
    this.#store.removeItem(this.#key(key));
  }

  clear(): void {
    for(const key of this.#keys())
      this.#store.removeItem(key);
  }

  key(i: number): string | null {
    return this.#keys()[i]?.slice(this.#prefix.length + 1) ?? null;
  }

  get length(): number {
    return this.#keys().length;
  }
}