ReactJS API Data Fetching CORS error

The CORS settings need to be setup in the API to allow access from your React app domain. No CORS settings, no AJAX from different domains. It's simple as that. You can either add CORS settings to your company API (this is unlikely to happen) or you can work around like described below:

The CORS is solely a mechanism of client browser to protect users from malicious AJAX. So one way to work around this is proxying your AJAX request from your React app to its own web server. As Vincent suggests, the create-react-app provides an easy way to do this: in your package.json file, simply chuck "proxy": "http://your-company-api-domain". For more details, please see this link

Then in your react app you can using relative URL like this: fetch('/api/endpoints'). Notice that the relative URL has to match with your company API. This will send a request to your server, then the server will forward the request to your company API and return the response back to your app. Since the request is handled in the server-to-server way not browser-to-server so the CORS check won't happen. Therefore, you can get rid of all unnecessary CORS headers in your request.