> For the complete documentation index, see [llms.txt](https://openai.gitbook.io/code-cheatsheets/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://openai.gitbook.io/code-cheatsheets/js/webjs/cors.md).

# CORS

Cross-Origin Resource Sharing ([CORS](https://developer.mozilla.org/en-US/docs/Glossary/CORS))

By default, requests are blocked if not same origin

**SERVER** must be configured to return the resource with the `Access-Control-Allow-Origin: *` or the specific domain you wish to allow

All non idempotent(besides GET and some POSTS with specific meme) will be first fetched with an OPTIONS

Express => <https://expressjs.com/en/resources/middleware/cors.html>

Flask => <https://flask-cors.readthedocs.io/en/latest/#using-json-with-cors>

*Sometimes you can get CORS errors because of having/not having a trailing slash (something about redirects not being allowed idk)*