I've been trying to make these code works what I expected, but it doesn't really works what I expected

import fetch from 'node-fetch';
const BASE_URL = 'https://estra-api.herokuapp.com/';

let EstraLoader = class Estra {
    loadAPI() {
        var data = '';
        fetch(BASE_URL)
        .then(function (response) {
        return response.json();
    })
        .then(function (myJson) {
        data = myJson;
        return data["Version"];
    });
}};

let EstraJS = new EstraLoader();
console.log(EstraJS.loadAPI());

The output always undefined, is there anything I can change from this codes that I made?

All I did want was the return data["Version"]; gives output by using console.log(EstraJS.loadAPI());