How do I make the method return the text value of an element on the page, using Selenium with JS? Now returns undefined

homepage.js

const { Builder, By, Key, until } = require('selenium-webdriver');
let Basepage = require('../pageobjects/basepage');
    
class Homepage extends Basepage {
    
 isAviasales(){
         driver.findElement(By.xpath("//h1[@class='header__title']")).getText().then(function(txt){
             return txt+'';});
        }
module.exports = new Homepage();

basepage.js

    let webdriver = require('selenium-webdriver');
let driver = new webdriver.Builder().forBrowser('chrome').build();
driver.manage().setTimeouts( { implicit: 10000 } );

class Basepage{
    constructor(){
        global.driver = driver;
    }

   go_to_url(theURL){
       return driver.get(theURL);      
    }
}

module.exports = Basepage;

testpage.js

const assert = require('chai').assert;
const homepage = require('../pageobjects/homepage');
let baseurl = 'https://www.aviasales.by/';

describe('Tests are starting', function(){
      this.timeout(7000);
   
    it('Mainpage test',function(){
        
        homepage.go_to_url(baseurl);
     // assert.equal(homepage.isAviasales(),'Поиск дешёвых авиабилетов');
    })

    it('Omsk test',function(){                     
        homepage.enterText('Омск');
      //  assert.equal(homepage.isOMS(),'OMS');
    })

    it('Swap test',function(){                
       homepage.clickSwapPlaces();
    })
})

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