[javascript] Encrypt data in javascript browser as base64 code without padding

encrypt.js

export const encode = (str) =>
  btoa(str).replace(/\+/g, '-').replace(/\//g, '_').replace(/\=+$/, '');

export const decode = (str) => {
  if (str.length % 4 != 0) {
    str += '==='.slice(0, 4 - (str.length % 4));
  }
  return atob(str.replace(/-/g, '+').replace(/_/g, '/'), 'base64');
};

export const encrypt = async (plaintext, password) => {
  try {
    const pwUtf8 = new TextEncoder().encode(password); // encode password as UTF-8
    const pwHash = await crypto.subtle.digest('SHA-256', pwUtf8); // hash the password

    const iv = crypto.getRandomValues(new Uint8Array(12)); // get 96-bit random iv
    const ivStr = Array.from(iv)
      .map((b) => String.fromCharCode(b))
      .join(''); // iv as utf-8 string

    const alg = { name: 'AES-GCM', iv: iv }; // specify algorithm to use

    const key = await crypto.subtle.importKey('raw', pwHash, alg, false, [
      'encrypt',
    ]); // generate key from pw

    const ptUint8 = new TextEncoder().encode(plaintext); // encode plaintext as UTF-8
    const ctBuffer = await crypto.subtle.encrypt(alg, key, ptUint8); // encrypt plaintext using key

    const ctArray = Array.from(new Uint8Array(ctBuffer)); // ciphertext as byte array
    const ctStr = ctArray.map((byte) => String.fromCharCode(byte)).join(''); // ciphertext as string

    return encode(ivStr + ctStr); // iv+ciphertext base64-encoded
  } catch (error) {
    throw error;
  }
};

export const decrypt = async (ciphertext, password) => {
  try {
    const pwUtf8 = new TextEncoder().encode(password); // encode password as UTF-8
    const pwHash = await crypto.subtle.digest('SHA-256', pwUtf8); // hash the password

    const ivStr = decode(ciphertext).slice(0, 12); // decode base64 iv
    const iv = new Uint8Array(Array.from(ivStr).map((ch) => ch.charCodeAt(0))); // iv as Uint8Array

    const alg = { name: 'AES-GCM', iv: iv }; // specify algorithm to use

    const key = await crypto.subtle.importKey('raw', pwHash, alg, false, [
      'decrypt',
    ]); // generate key from pw

    const ctStr = decode(ciphertext).slice(12); // decode base64 ciphertext
    const ctUint8 = new Uint8Array(
      Array.from(ctStr).map((ch) => ch.charCodeAt(0))
    ); // ciphertext as Uint8Array
    // note: why doesn't ctUint8 = new TextEncoder().encode(ctStr) work?

    const plainBuffer = await crypto.subtle.decrypt(alg, key, ctUint8); // decrypt ciphertext using key
    const plaintext = new TextDecoder().decode(plainBuffer); // plaintext from ArrayBuffer
    return plaintext; // return the plaintext
  } catch (e) {
    throw e;
  }
};