Pre-flighted JavaScript requests

POST request with correct CORS setup


JavaScript code can make a cross-origin POST request. Since there is a Content-Type header of application/json, the browser sends a pre-flight request.

The pre-flight response must include these correctly configured headers.

The response to the main request must also include the Access-Control-Allow-Origin header.


  1. Press F12 to open browser Developer Tools
  2. Open Network tab and filter by path post-success
  3. Hit green button below and observe 1 pre-flight and 1 main request
View source on GitHub | Created by Tom Gregory