What is equivalent to the following inside a successful XHR request?

Question

I posted a question about a less specific topic earlier, located here: Redirect response to download file

You can read the details there if you'd like.

Tim gave me a good answer to just set the document.location.href = '/genericHandlers/DownloadFile.ashx?id=' + this.model.get("id"); and just use a GET rather than the POST I originally thought.

The only problem with this approach is that I cant gracefully fail if the file isnt found. So my question now is:

What, inside the XHR object, is equilvent to Tim's answer? Basically, all I want to do is begin the download. Ive tried:

document.location.href = xhr.getAllResponseHeaders();

But that obviously doesnt work. Any ideas?

Answer 1

You can first make an AJAX request to see if the page will return a 404 error or not. This creates performance and bandwidth issues though.

This question has answers with the implantation details: How can I check existence of a file with JavaScript?