GramJS

const { Api, TelegramClient } = require("telegram");
const { StringSession } = require("telegram/sessions");

const session = new StringSession(""); // You should put your string session here
const client = new TelegramClient(session, apiId, apiHash, {});

(async function run() {
  await client.connect(); // This assumes you have already authenticated with .start()

  const result = await client.invoke(
    new Api.contacts.ImportContacts({
      contacts: [
        new Api.InputPhoneContact({
          clientId: readBigIntFromBuffer(generateRandomBytes(8)),
          phone: "some string here",
          firstName: "some string here",
          lastName: "some string here",
        }),
      ],
    })
  );
  console.log(result); // prints the result
})();

import { Api, TelegramClient } from "telegram";
import { StringSession } from "telegram/sessions";

const session = new StringSession(""); // You should put your string session here
const client = new TelegramClient(session, apiId, apiHash, {});

(async function run() {
  await client.connect(); // This assumes you have already authenticated with .start()

  const result: Api.contacts.ImportedContacts = await client.invoke(
    new Api.contacts.ImportContacts({
      contacts: [
        new Api.InputPhoneContact({
          clientId: readBigIntFromBuffer(generateRandomBytes(8)),
          phone: "some string here",
          firstName: "some string here",
          lastName: "some string here",
        }),
      ],
    })
  );
  console.log(result); // prints the result
})();