Return string function Javascript

Question

function getLinks(param) {
  let url = 'http://localhost/site/feed.php?url=' + param;
  let request = new XMLHttpRequest();
  let text = "";
  request.responseType = 'text';
  request.onload = function(event) {
    let obj = request.responseText;
    console.log(obj); // Returns: https://some.php.link.php
    console.log(typeof obj); // Returns: string
    return obj;
  };
  request.open('GET', url, true);
  request.send();
}

function getDeals() {
        let url = getLinks('deals_feed');
        console.log(url); // Returns: undefined
    }
getDeals();

Why is this happening? First two console logs from getLinks() are how it should, but when I call it from the getDeals function, I get undefined.