Global variable won't change inside of a function

Question

I ran into a problem with my JS project. I declared a global variable:

var agencies = {};

And I have a function:

function getAllAgencies() {
  let request = new XMLHttpRequest();
  request.onreadystatechange = function () {
    console.log(this.readyState);
    console.log(this.status);

    if (this.readyState == 4) {
      if (this.status == 200) {
        agencies = JSON.parse(request.responseText);
      } else {
        alert("Greska prilikom ucitavanja agencije!");
      }
    }
  };
  request.open("GET", firebase + "/agencije.json", true);
  request.send();
}

However, after I call this function it doesn't change the value of the variable agencies, it's still {}.

I checked, it goes into the if statements