title: jQuery Ajax access custom response headers
body: <p>I'm using some API, and I noticed that in the response I have this:</p>
  
  <p><a href="https://i.stack.imgur.com/1i0E6.png" rel="noreferrer"><img src="https://i.stack.imgur.com/1i0E6.png" alt="Chrome Console Screen"></a></p>
  
  <p>I'd need to read the "x-dl-units-left", but I get null:</p>
  
  <pre><code>$.ajax(ajaxConfig).done(function(response, textStatus, xhr){
    var left = xhr.getResponseHeader("x-dl-units-left"); //null
    var all = xhr.getAllResponseHeaders(); // "content-type: application/json;charset=UTF-8"
  });
  </code></pre>
  
  <p>Anyone who might know why?? :(</p>
  
  <p>Thank you</p>