gistfile1.txt

// helper methods starts

var lc = ["0", "1", "2", "3", "4", "5", "6", "7",
          "8", "9", "a", "b", "c", "d", "e", "f"];
var uc = ["0", "1", "2", "3", "4", "5", "6", "7",
          "8", "9", "A", "B", "C", "D", "E", "F"];

function toHex(val, uppercase) {
  var set = uppercase ? uc : lc;
  return set[Math.floor(val / 16)] + set[val % 16];
}


function toArrayBuffer(str) {
  str = str.toLowerCase().replace(/\s/g, "");
  if (str.length % 2 == 1)
    str = "0" + str;

  var len = Math.floor(str.length / 2);
  var buffer = new Uint8Array(len);

  var curr = -1;
  for (var i = 0; i < str.length; ++i) {
    var c = str[i];
    var val = lc.indexOf(c);
    if (val == -1)
        throw Error("unexpected character")

    if (curr === -1) {
      curr = 16 * val;
    } else {
      buffer[Math.floor(i / 2)] = curr + val;
      curr = -1;
    }
  }

  return buffer;
}

function toString(arr, opts) {
  var defaultOpts = {
    grouping: 0,
    rowlength: 0,
    uppercase: true,
  };

  if (opts == undefined)
    opts = {}

  opts = defaultOpts;

  var str = "";
  var group = 0, column = 0;
  for (var i = 0; i < arr.length; ++i) {
    str += toHex(arr[i], opts.uppercase);

    if (i === arr.length - 1)
      break;

    if (opts.grouping > 0 && ++group === opts.grouping) {
      group = 0;

      if (opts.rowlength > 0 && ++column === opts.rowlength) {
        column = 0;
        str += "\n";
      }
      else
        str += " ";
    }
  }

  return str;
}

const ab2str = buf => String.fromCharCode.apply(null, new Uint16Array(buf));
const ab2hex = ab => toString(new Uint8Array(ab));

const str2ab = str => {
  const buf = new ArrayBuffer(str.length*2); // 2 bytes for each char
  const bufView = new Uint16Array(buf);
  for (let i=0, strLen=str.length; i<strLen; i++) {
    bufView[i] = str.charCodeAt(i);
  }
  return buf;
}

// helper method ends

async function importCryptoKey(key){
  return await window.crypto.subtle.importKey(
    "raw", // can be "jwk" or "raw"
    toArrayBuffer(key).buffer,
    {name: 'AES-GCM'},
    true, // whether the key is extractable (i.e. can be used in exportKey)
    ["encrypt", "decrypt"] // can "encrypt", "decrypt", "wrapKey", or "unwrapKey"
  )
};

async function encrypt({ text, iv, key }){
  const arrayBuffer = await window.crypto.subtle.encrypt(
    {
      name: 'AES-GCM',
      iv: toArrayBuffer(iv).buffer,
    },
    await importCryptoKey(key),
    str2ab(text),
  );
  return ab2hex(arrayBuffer);
};

key = 'EEE72939E910F74104846B5BADBDDAD007A46E3392ADE713F6EE33900299C250'
iv = '523AEBE425EA83DCE42F9512'
data = '{"username":"test","password":"test"}'

res = await encrypt({text: data, iv, key});
console.log(res);

prints C7F3F0EA027EA0B75BF6286AD688497F265AF3AF10A8BA273B7AD9D9D3F1B6FD247E85771BAE4447F81447389A84A3145155E7DE387D6B3E181516707731EC2DC3CEF847FCA949EE484B3FC0A6C66853D42C956BA0735642D29E