getwebauthor.js

//Copy and get the getRequest method from url - https://gist.github.com/ktskumar/a9e9df497673e9fd26ead8532b9ff425
getRequest("https://domain.sharepoint.com/sites/name/_api/web?$expand=author").then(function(response) {
    var result = JSON.parse(response.responseText);
    console.log(result);
    alert("Site Auhtor: " + result.Author.Title);
});