How to execute a javascript function just before saving a wocommerce post or a post?

I am working on this project and I am trying to execute a jquery or javascript just before saving the post, I have tried the following:

 function do_something_with_a_post($id) {

 <script>alert('hello');</script>
 }
 add_action('pre_post_update', 'do_something_with_a_post');

but it gives a php error... I am really unsure on how to do this.

Does anyone has an idea? Thanks!