Response.redirected

The read-only redirected property of the Response interface indicates whether or not the response is the result of a request you made which was redirected.

A boolean value which is true if the response indicates that your request was redirected.

Checking to see if the response comes from a redirected request is as simple as checking this flag on the Response object. In the code below, a textual message is inserted into an element when a redirect occurred during the fetch operation. Note, however, that this isn't as safe as outright rejecting redirects if they're unexpected, as described under Disallowing redirects below.

fetch("awesome-picture.jpg").then(function(response) {
  let elem = document.getElementById("warning-message-box");
  if (response.redirected) {
    elem.innerHTML = "Unexpected redirect";
  } else {
    elem.innerHTML = "";
  }
  return response.blob();
}).then(function(imageBlob) {
  let imgObjectURL = URL.createObjectURL(imageBlob);
  document.getElementById("img-element-id").src = imgObjectURL;
});

Because using redirected to manually filter out redirects can allow forgery of redirects, you should instead set the redirect mode to "error" in the init parameter when calling fetch(), like this:

fetch("awesome-picture.jpg", { redirect: "error" }).then(function(response) {
  return response.blob();
}).then(function(imageBlob) {
  let imgObjectURL = URL.createObjectURL(imageBlob);
  document.getElementById("img-element-id").src = imgObjectURL;
});

• Fetch API
• ServiceWorker API
• HTTP access control (CORS)
• HTTP