safe_store.ts

import { AES } from "https://deno.land/x/god_crypto/aes.ts";
import { encode, decode } from "https://deno.land/std@0.97.0/encoding/hex.ts";

class SecretStore {
  #aes: AES;

  constructor(data: { key: string; iv?: string }) {
    this.#aes = new AES(data.key, {
      mode: "cbc",
      iv: data.iv ?? "random 16byte iv",
    });
  }

  async setItem(name: string, value: string): Promise<void> {
    const encryptedBytes = await this.#aes.encrypt(
      encode(new TextEncoder().encode(value))
    );
    const hash = encode(encryptedBytes);
    console.log(encryptedBytes.hex());

    localStorage.setItem(name, new TextDecoder().decode(hash));
  }

  async getItem(name: string): Promise<null | string> {
    const encrypted = localStorage.getItem(name);
    if (encrypted === null) return null;
    const decrypted = await this.#aes.decrypt(
      decode(new TextEncoder().encode(encrypted))
    );
    return new TextDecoder().decode(
      decode(decode(new TextEncoder().encode(decrypted.hex())))
    );
  }
}

const store = new SecretStore({ key: "thegrassisgreen_" });

await store.setItem("password", "foo");
console.log(localStorage.getItem("password"));
console.log(await store.getItem("password"));

Working now thanks to lucas 🎉