Response: redirected プロパティ

fetch("awesome-picture.jpg")
  .then((response) => {
    const elem = document.getElementById("warning-message-box");
    elem.textContent = response.redirected ? "予期しないリダイレクト" : "";
    // リダイレクト後の最終 URL
    console.log(response.url);
    return response.blob();
  })
  .then((imageBlob) => {
    const imgObjectURL = URL.createObjectURL(imageBlob);
    document.getElementById("img-element-id").src = imgObjectURL;
  });

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