xmlHttpreadyState == 4 && xmlHttpstatus == 200

This is a condition that checks if the XMLHttpRequest object's readyState property is equal to 4 (which means the request has been completed and the response is ready) and if the status property is equal to 200 (which means the request was successful). If both conditions are true, it indicates that the server has successfully responded to the request and returned a status code of 200, which typically means that the requested resource was found and returned successfully.