Question: Is it possible to prevent the browser from following redirects when sending XMLHttpRequest-s (i.e. to get the redirect status code back and handle it myself)?

Answer: 
The new [Fetch API](https://developer.mozilla.org/en-US/docs/Web/API/Fetch_API) supports different modes of redirect handling: `follow`, `error`, and `manual`, but I can't find a way to view the new URL or the status code when the redirection has been canceled. You just can stop the redirection itself, and then it looks like an error (empty response). If that's all you need, you are good to go. Also you should be aware that the requests made via this API are not cancelable [yet](https://github.com/whatwg/fetch/issues/27). *They [are](https://stackoverflow.com/a/46785332) now.*

As for XMLHttpRequest, you can `HEAD` the server and inspect whether the URL has changed:

```
var http = new XMLHttpRequest();
http.open('HEAD', '/the/url');
http.onreadystatechange = function() {
    if (this.readyState === this.DONE) {
        console.log(this.responseURL);
    }
};
http.send();

```

You won't get the status code, but will find the new URL without downloading the whole page from it.
You can use `responseURL` property to get the redirect destination or check whether the response was ultimately fetched from a location you accept. 

This of course means the result is fetched anyway, but at least you can get the necessary info about the redirect destination and for example detect conditions when you would like to discard the response.