How to substitute js response data in sql query?

Question

MySQL

I have a sql query

$qwe = $pdo->prepare("SELECT * FROM podkategories WHERE idcat='???'");

And there is a value from the value tag of the
value I selected How to substitute data from js into sql ??
$("#catid").val();

Answer 1

Send via ajax.
Transfer simply getom.
Directly from JS to php - no way.