How to redirect to calling page if Javascript fetch gets a redirect

I have a case where I’m calling fetch() and if the response is a 302 Redirect, I want to redirect the calling page to wherever it redirects to instead of following the redirect to retrieve the data.

The scenario is that the user does something on a page which is going to do a fetch to retrieve something to update on the page. But if their login session has expired, the server is going to return a 302 Redirect to the login page. My Javascript is expecting a JSON response back, but instead fetch follows the redirect and it gets an HTML page.
What I really want to do is check if the response.status is 302, get the URL that the redirect pointed to and set window.location.

According to the documentation, I should be able to set redirect: "manual", then if the response.redirected is true redirect to response.url, or some say to retrieve the location header from the response

But none of that works.

• response.redirected is never true.
• response.status is zero.
• response.url is the URL of the page that made the call, not where it was redirected to.
• The location header is null.

The only thing that seems to work is that the Network tab shows that the server returned a 302 status.
Here’s my code:

   fetch("url-that-forces-a-redirect", {
       method: "POST",
       redirect: "manual",
       body: formData
    }).then((response) => {
       console.log("Response had status " + response.status);
       if (response.redirected) {
           var redirectedUrl = response.headers.get('location');
           console.log("Got redirect: location header = " + redirectedUrl);
           console.log("                 response.url = " + response.url);
           // window.location = redirectedUrl;
           return;
       }
    });

Is there any way to do this?

BTW, I tried doing this with XMLHttpRequest first and couldn’t find a way to do it there either.