Why Am I Getting HTTP 5xx/4xx Errors with \'No \'Access-Control-Allow-Origin\' Header\'?

HTTP 5xx or 4xx Error with "No 'Access-Control-Allow-Origin' Header is Present"

Problem:

You are receiving HTTP 5xx or 4xx errors when making cross-origin requests from a web application to an Express Node application. The error message indicates that the "Access-Control-Allow-Origin" header is missing from the response.

Background:

Cross-origin resource sharing (CORS) is a mechanism that allows resources on a web page to be requested from another domain. To enable CORS, the server must send certain headers in the response, including the "Access-Control-Allow-Origin" header.

Cause:

The 5xx or 4xx error can have multiple causes, but it often indicates a problem on the server side. To identify the cause, it's essential to check the server logs for any error messages.

CORS Header

The "Access-Control-Allow-Origin" header is only sent by the server for successful requests (2xx and 3xx responses). For 5xx or 4xx errors, the server typically does not send this header.

Resolution:

To resolve the error, it's crucial to determine the underlying cause, which can be done by inspecting server logs. Once the root cause is identified, it can be addressed, such as:

• Fixing issues with the server-side code that handles the requests
• Ensuring that the web application sends the appropriate CORS-related headers
• Configuring the web application to use "no-cors" mode (only if the request is considered safe)

By addressing the underlying cause, you can eliminate the 5xx or 4xx error and ensure that the "Access-Control-Allow-Origin" header is sent for valid requests.

The above is the detailed content of Why Am I Getting HTTP 5xx/4xx Errors with \'No \'Access-Control-Allow-Origin\' Header\'?. For more information, please follow other related articles on the PHP Chinese website!