【問題】js fetch和 cors policy ---header Access-Control-Allow-Origin 問題

const getRawData = (URL) => {

   return fetch(URL, {

         method: "GET",

         mode: 'cors',

         headers:{'Access-Control-Allow-Origin':'*'},

         

      })

      .then((response) => response.text())

      .then((data) => {

         return data;

      });

};

瀏覽器上:

from origin 'null' has been blocked by CORS policy: Response to preflight request doesn't pass access control check: No 'Access-Control-Allow-Origin' header is present on the requested resource. If an opaque response serves your needs, set the request's mode to 'no-cors' to fetch the resource with CORS disabled.

但是我Access-Control-Allow-Origin已經加入header了 請問有人看出是哪裡出問題了嗎(是Local server 所以排除security issue)