PHP filter_has_var

filter_has_var - Checks if variable of specified type exists

 filter_has_var ( int $type , string $variable_name ) : bool

Parameters
type - One of INPUT_GET, INPUT_POST, INPUT_COOKIE, INPUT_SERVER, or INPUT_ENV.
variable_name - Name of a variable to check.

Types of filters
Validate filters
Sanitize filters
Other filters
Filter flags

Checking  isset($_POST['user']) will produce: Warning "Do Not Access Superglobal $_POST Array Directly." in Netbeans or Apache Netbeans for PHP.

if (isset($_POST['user'])) {
  $user = $_POST['user'];
}

you can use php filter_has_var and filter_input

if (filter_has_var(INPUT_POST, 'user')) {
 $user = filter_input(INPUT_POST, 'user');
}

Links:
PHP filter_input