TypeError when trying to refactor

I'm trying to refactor a test, and I can't figure out what I'm doing wrong.

So, trying to refactor from this example :

Test.ts

import MailosaurClient from "mailosaur";
import { Selector, t } from "testcafe";
const testUrl = `https://www.google.com/`;
fixture("fixture")
  .page("https://www.google.com/")
  .beforeEach(async (t) => {
    console.log("test");
  })

test("Test", async (t) => {
  console.log("Starting test");
     await t.expect(getUrl()).eql(url);
}

to this:

MainApp.ts

const getUrl = ClientFunction(() => window.location.href);
export class MainApp {
  async login(url:string) {
    await t.expect(getUrl()).eql(url);
  }} 

Test.ts

import MailosaurClient from "mailosaur";
import { Selector, t } from "testcafe";
import {MainApp} from "./MainApp";
const testUrl = `https://www.google.com/`;
fixture("fixture")
  .page("https://www.google.com/")
  .beforeEach(async (t) => {
    console.log("test");
  })
const mainApp = new MainApp();
test("Test", async (t) => {
  console.log("Starting test");
  await MainApp.login(
    testUrl
  ); }

but unexpectedly this error occurs :

"Cannot prepare tests due to the following error:

TypeError: MainApp_1.MainApp is not a constructor"