Magento 2: How to show loader while customer-data is loading from server?

Question

  define([
    'Magento_Ui/js/form/form',
    'Magento_Customer/js/customer-data'
], function (Component, customerData) {
   'use strict';

    return Component.extend({
        isLoggedIn: function () {
           this.customer = customerData.get('customer');
           if (!this.customer().firstname) {
              return false;
           }
           return true;
       }
    });

}

When the customer login and the customer data is being loaded by ajax from server, isLoggedIn returns false.

But this is not correct as the customer has logged in and local-storage update is in progress.

How to get the logged in state while data is loading from server in 'customer-data.js'?