Request.onload = answer;
Request.open("post", "https://xxx.php", false);
Request.setRequestHeader("Content-Type","application/x-www-form-urlencoded; charset=utf-8");
Request.send(forSend);

header('Content-Type: application/json');
header('X-Content-Type-Options nosniff');
header('Access-Control-Allow-Origin: *');
header('Access-Control-Allow-Methods: POST');
header('Access-Control-Allow-Headers: Content-Type');
header('Access-Control-Allow-Credentials: true');

Failed to load https://xxx.php: No 'Access-Control-Allow-Origin' header is present on the requested resource. Origin 'null' is therefore not allowed access.
Uncaught DOMException: Failed to execute 'send' on 'XMLHttpRequest': Failed to load 'https://xxx.php'.