Trapping WordPress errors with output buffering.
If you have tried to use AJAX with WordPress, most likely you have stumbled upon the wp_die() function which completely kills the response you expect to get. However, we can trap the wp_die() by using PHP’s output buffering and the ob_start callback function to process the output of wp_die() even though a die() is called. This is a very special case, and will only work when you are able to ensure output buffering can be called before the die is called.
The easiest way to get a non-fatal wp_die() error (an error that shouldn’t cause the entire application to stop) is when submitting comments: non-fatal errors occur whenever someone posts too quickly or submits a duplicate comment, so this can be a problem when creating an AJAX app to submit comments (I ran into this problem with INAP.)
Since AJAX makes the entire submit process very quick, so it is easy to trigger the “Posting too quickly” error if the user make short comments, and when this happens an entire page –complete with CSS and headers– is returned as the AJAX response.
