Answers for "has been blocked by CORS policy: Request header field content-type is not allowed by Access-Control-Allow-Headers in preflight response"

has been blocked by CORS policy: Request header field content-type is not allowed by Access-Control-Allow-Headers in preflight response.

response.setHeader("Access-Control-Allow-Origin", "*");
response.setHeader("Access-Control-Allow-Credentials", "true");
response.setHeader("Access-Control-Allow-Methods", "GET,HEAD,OPTIONS,POST,PUT");
response.setHeader("Access-Control-Allow-Headers", "Access-Control-Allow-Headers, Origin,Accept, X-Requested-With, Content-Type, Access-Control-Request-Method, Access-Control-Request-Headers");

Angular Laravel has been blocked by CORS policy: Request header field x-requested-with is not allowed by Access-Control-Allow-Headers in preflight response.

namespace App\Http\Middleware;
use Closure;
class Cors
{
    public function handle($request, Closure $next)
    {
        $response = $next($request);
        $response->header('Access-Control-Allow-Methods', 'HEAD, GET, POST, PUT, DELETE');
        $response->header('Access-Control-Allow-Headers', $request->header('Access-Control-Request-Headers'));
        $response->header('Access-Control-Allow-Origin', '*');
        return $response;
    }
}

has been blocked by CORS policy: Request header field content-type is not allowed by Access-Control-Allow-Headers in preflight response

var dataToSend = ' {"firstname": "' + form.vals().FirstName + '","lastname": "' + form.vals().LastName + '","email": "' + form.vals().Email + '"}';
var xhr = new XMLHttpRequest();
xhr.open('POST', 'https://exampleurl');
xhr.setRequestHeader('Content-type','application/json');
xhr.send(dataToSend);
xhr.onreadystatechange = function() {
  if (this.readyState == 4 && this.status == 200) {
	console.log(this.responseText);
  }
};



xhr.setRequestHeader("Access-Control-Allow-Origin", "*");
xhr.setRequestHeader("Access-Control-Allow-Credentials", "true");
xhr.setRequestHeader("Access-Control-Allow-Methods", "GET,HEAD,OPTIONS,POST,PUT");
xhr.setRequestHeader("Access-Control-Allow-Headers", "Access-Control-Allow-Headers, Origin,Accept, X-Requested-With, Content-Type, Access-Control-Request-Method, Access-Control-Request-Headers");