Prevent attachment from being deleted

Question

In Wordpress admin media library page (upload.php) I'd like to do some checking on delete_attachment action.

I want my custom function to fire before attachment's being deleted.

In this function I want to check for it's relations with another objects in database. And delete it only if there are no relations at all.

I use this code (in functions.php) to see if my function is fired on delete_attachment:

add_action( 'delete_attachment', 'check_relations' );
function check_relations( $post_id ){
    ?>  
    <script>
        function myFunction() {
            alert("Hello! I am an alert box!");
        }
    </script>
    <?php
}

but it seems that my function's not firing at all. And image attachment is being completely deleted. What's wrong in this code?

Answer 1

Have you seen this ? https://stackoverflow.com/a/28429009/3967385

Actually you can't fire JavaScript with php simply like that.