react-解決 fetch 跨域問題：Access to fetch at XXX from origin YYY has been blocked by CORS policy

參考連結（對我沒用）：
https://blog.csdn.net/qq_41956139/article/details/106564357

https://blog.csdn.net/weixin_44415625/article/details/87607924?utm_medium=distribute.pc_relevant.none-task-blog-BlogCommendFromMachineLearnPai2-3.channel_param&depth_1-utm_source=distribute.pc_relevant.none-task-blog-BlogCommendFromMachineLearnPai2-3.channel_param

1. 在post請求裡新增請求體：

   static post(url, data){
       return new Promise((resolve, reject) =>{
           fetch(url,{
               method:'POST',
               headers:{
                   'Accept':'application/json',
                   'Content-Type':'application/json',
                   'Access-Control-Allow-Origin':'*',
                   'Access-Control-Allow-Headers': 'Origin, X-Requested-With, Content-Type, Accept',
                   'Access-Control-Allow-Methods': 'PUT,POST,GET,DELETE,OPTIONS'
               },
               body:JSON.stringify(data)
           })
               .then(response=>response.json())
               .then(result=>resolve(result))
       })
   }
   

2. 在response的py檔案中新增請求頭部

   @app.route('/data', methods=['POST'])
   def getInfo():
       response = Response("data")
       response.headers.set('Access-Control-Allow-Origin', '*')
       response.headers.set('Access-Control-Allow-Methods', 'GET, POST')
       data = request.get_data(as_text=True)
       re = {
       'code': 0,
       'data':data,
       'message': "這是測試呀"
       }
       print("後端資料：", data)
       return json.dumps(re)
   

上面的都沒啥用！！！

有用的解決辦法：

import flask
from flask import Flask, request, jsonify, Response, make_response
import json
from flask_cors import *

app = Flask(__name__, template_folder='../frontend', static_folder='../frontend', static_url_path='')

#看這裡！
CORS(app, supports_credentials=True)