gramjs/examples/simpleLogin.js

const phoneDiv = document.getElementById("phoneDiv");
const phone = document.getElementById("phone");
const phoneSend = document.getElementById("phoneSend");
const codeDiv = document.getElementById("codeDiv");
const code = document.getElementById("code");
const codeSend = document.getElementById("codeSend");
const passDiv = document.getElementById("passDiv");
const pass = document.getElementById("pass");
const passSend = document.getElementById("passSend");
const logger = document.getElementById("log");

function phoneCallback() {
  phone.disabled = false;
  phoneSend.disabled = false;

  return new Promise((resolve) => {
    phoneSend.addEventListener("click", function () {
      phone.disabled = true;
      phoneSend.disabled = true;
      resolve(phone.value);
    });
  });
}

function passwordCallback() {
  passDiv.style.visibility = "visible";

  return new Promise((resolve) => {
    passSend.addEventListener("click", function () {
      code.disabled = true;
      codeSend.disabled = true;

      resolve(pass.value);
      alert("welcome");
    });
  });
}

function codeCallback() {
  code.disabled = false;
  codeSend.disabled = false;

  codeDiv.style.visibility = "visible";

  return new Promise((resolve) => {
    codeSend.addEventListener("click", function () {
      code.disabled = true;
      codeSend.disabled = true;
      resolve(code.value);
    });
  });
}

const { TelegramClient } = gramjs;
const { StringSession } = gramjs.sessions;
const apiId = 1; // put your api id here [for example 123456789]
const apiHash = "1  "; // put your api hash here [for example '123456abcfghe']

const client = new TelegramClient(new StringSession(""), apiId, apiHash, {
  connectionRetries: 3,
}); // you can pass a string session here from previous logins.
// If you want to run this example in the test servers uncomment this line
// client.session.setDC(2, '149.154.167.40', 80)

client
  .start({
    botAuthToken: phoneCallback,
  })
  .then(() => {
    console.log("%c you should now be connected", "color:#B54128");
    console.log(
      "%c your string session is " + client.session.save(),
      "color:#B54128"
    );
    console.log(
      "%c you can save it to login with it next time",
      "color:#B54128"
    );
  });