I have a text input field and on focusout I send a post request to the backend using $.ajax();. How do I show the browser popup which asks people if they are sure to leave the page when the $.ajax() request is still going on in the background?

We can use the beforeunload event to ask the user if they are sure to leave the page, but I want to show that popup only when the post request from $.ajax() is still going on and not complete. How can I do that?

Thank you