What is the problem with Ajax onprogress?

Question

JavaScript

JS code:

$.ajaxSetup({
  xhr: function(){
    var xhr = new XMLHttpRequest();
    xhr.addEventListener("progress", function(data){
                     console.log(data.loaded, data.total);
                });
    return xhr;
  }
});

$.ajax({
  url : "file.txt",
  success : function(){ alert("!") }
});

What is in the file file.txt ? - It just contains text for the test, the file weighs 20mb.

Running the code above, I get in the console only something like 20мб, 20мб. Why does onprogress work only once, and even then, at the very end?

Answer 1

jsfiddle.net/r86gM/9 is a good example