This error typically occurs in web development when making cross-origin requests. This error is related to the same-origin policy implemented by web browsers for security reasons. The same-origin policy restricts web pages from making requests to a different domain unless the server explicitly allows it by including the ‘Access-Control-Allow-Origin’ header in the response. To resolve this issue, the server hosting the requested resource needs to include the appropriate ‘Access-Control-Allow-Origin’ header, specifying the domain or origins allowed to access the resource. This can be done by configuring the server’s response headers or by using server-side middleware or frameworks that handle cross-origin requests.
JSON with Padding is just a way to circumvent same-origin policy, when CORS is not an option. This is risky and a bad practice. Avoid using this.
If you want to bypass that restriction when fetching the contents with fetch API or XMLHttpRequest in javascript, you can use a proxy server so that it sets the header Access-Control-Allow-Origin to *.
If you need to enable CORS on the server in case of localhost, you need to have the following on request header.
Access-Control-Allow-Origin: http://localhost:9999