You've created an XMLHttpRequest object, xhr, and properly called open as well as send on the object. When you check xhr.status and it's 0 and your responseText is null. What's the most likely explanation of what happened?

How do you detect errors in Ajax REQUESTS?

What XMLHttpRequest method is used to override MIME type returned by the server?

How does JSONP work?

What HTML attribute would you use to indicate to a screenreader that an element of the page may update (for example, by using Ajax) while out of the user's focus?

When receiving an image from the server, the responseType attribute of your XMLHttpRequest object must be set to:

Which benefit can AJAX provide to Web Applications?

Which is the correct way to assign events to HTML elements using JavaScript?

Which request object method can be assigned a callback function which will be called every time the server updates the browser on the request its processing?

How to use Basic Auth with jQuery and AJAX?aja

Which may be a disadvantage of using AJAX?