Can one hook in wp_head inside other hook?

Question

I have to add some scripts in the head part of our website whenever a login or registration of a user was successful. For the login and register forms we use the Ultimate Member plugin, which has a hook method um_user_login and um_user_register which I though I could use for that.

I.e. if a user login was successful, do an head.append(...) in JavaScript.

However I am a NodeJS and Java developer and completely new to Wordpress plugin programming. I can't find a suitable solution so far for this easy sounding task.

My idea was to hook at the um_user_login action and do something like:

add_action('um_user_login', 'add_tracking_after_login', 10);

function add_tracking_after_login() {
    add_action('wp_head', function() {
        echo '<script type="text/javascript" src="my_script.js"></script>';
    });
}

However, I have tested this with different logging, but it seems like the hook function to wp_head is never executed (the function add_tracking_after_login is, as I have tested this with logging as well). So I think, I cannot add an action to wp_head this way.

Is there any other way to achieve the requested functionality? Or am I doing the hooking wrong as I am new to WordPress plugin programming?

Edit: To keep confusion low, this is just one of several tasks the client has requested. I also need to react on successful registrations and on successful sent emails with our contact form. In these cases I can't find an analogous workaround as in the answer below of Harry SM. I need to react on success events of the plugins we use.

Thanks in advance and best regards

Answer 1

you can add a condition for logged in user under wp_head hook.

add_action('wp_head', 'add_tracking_after_login', 10);

function add_tracking_after_login() {
    if ( is_user_logged_in() ) {
        echo '<script type="text/javascript" src="my_script.js"></script>';
    }
}