'Access-Control-Allow-Origin' issue when API call made from React (Isomorphic app)

CORS is a browser feature. Servers need to opt into CORS to allow browsers to bypass same-origin policy. Your server would not have that same restriction and be able to make requests to any server with a public API. https://developer.mozilla.org/en-US/docs/Web/HTTP/Access_control_CORS

Create an endpoint on your server with CORS enabled that can act as a proxy for your web app.

Use the google Chrome Extension called Allow-Control-Allow-Origin: *. It modifies the CORS headers on the fly in your application.

Fix Without Using External Proxy or Chrome Extension

CORS should be enable in server side! if you can not activate it on server (for example using external API) create a middleware React -> Middleware -> Orginal Server.

1. Create a Node.js project (Middleware) and use below code in app.js.

   const express = require("express");var cors = require('cors')const app = express();app.use(cors());const { createProxyMiddleware } = require('http-proxy-middleware');app.use('/api', createProxyMiddleware({     target: 'http://localhost:8080/', //original url    changeOrigin: true,     //secure: false,    onProxyRes: function (proxyRes, req, res) {       proxyRes.headers['Access-Control-Allow-Origin'] = '*';    }}));app.listen(5000);

This will pass the request http://localhost:5000/api/xxx to original server (for example http://localhost:8080/api/xxx), and returns the result to client.

2. Change client (React) to call proxy and get data without CORS error (you only need to change the port in url):

   axios.get('http://localhost:5000/api/xxx', //proxy uri{   headers: {      authorization: ' xxxxxxxxxx' ,      'Content-Type': 'application/json'   } }).then(function (response) {   console.log(response);});

3. run node project node app.js and react project npm start.