I'm new to TypeScript (and JavaScript) and I'm having some issues to wait until a function from an external library, namely amazon-cognito-identity-js is executed. I want to first authenticate an user and then get a token from that user. That's it. I read this nice tutorial about Promises and there is also an example on the official page of the library, but seems like I'm missing something.

I created the following code:

import {
  AuthenticationDetails,
  CognitoUser,
  CognitoUserPool
} from "amazon-cognito-identity-js";

var DEV_USER_POOL_DATA = {
  UserPoolId: 'userPool',
  ClientId: 'clientId'
};

var USER_POOL_DATA = DEV_USER_POOL_DATA;

function getJWT() {
  return new Promise<void>((resolve) => { 
    resolve();
  });
}

function login() {
  let userPool = new CognitoUserPool(USER_POOL_DATA);
  let authenticationDetails = new AuthenticationDetails({
    Username: "myUser",
    Password: "myPass",
  });
  let cognitoUser = new CognitoUser({ Username: "myUser", Pool: userPool });

  cognitoUser.authenticateUser(authenticationDetails, {
    onSuccess: function(result) {
      return result.getAccessToken().getJwtToken();
    },
    onFailure: function(err) {
      console.log(err); 
    }
  });
}

getJWT().then(login);
console.log('Hello world');

However when I run the code I see

Hello world
<The actual token I will like to see first>

Do you know what is wrong?