I am writing a web app on localhost:3000. When I tried to send a XMLHttpRequest to index.pup on the same host and port, I've got this error:

XMLHttpRequest at 'localhost:3000' from origin 'http://localhost:3000' has been blocked by CORS policy: Cross origin requests are only supported for protocol schemes: http, data, chrome, chrome-extension, chrome-untrusted, https.

How can I fix it?