print script on wordpress header after user registered

Question

I should attach javascript snipet after user is registered on my wordpress site, i user the user_register hook like this

do_action('user_register', $user_id );
add_action('user_register', 'MY_Callback');
function MY_Callback(){
  $data['user_id'] = $user_id;
  My_print_js($data);
}

Then in my My_print_js function

function My_print_js(){
   global $data;
   echo '<script>';
   echo 'dlayer.push('.json_encode($data).')'
   echo '</script>';
}

With that the script isn't printed after user_register, i have missed something? i note that i user woocommerce too.

Thank you guys and girls for helps :)

Answer 1

There's quite a few issues here:

do_action('user_register', $user_id );

No need to fire the action yourself (especially with an undefined variable $user_id) - the idea of actions & filters is that you "hook" your function to one, and then let WordPress trigger it when applicable.

function MY_Callback(){
  $data['user_id'] = $user_id;
  My_print_js($data);
}

Again $user_id is undefined (null) - you need to accept it as a parameter in your function:

function MY_Callback( $user_id ) {

Same issue again with your second function - you call it with a parameter (as above), but then completely ignore it and try to use the global $data - instead you want:

function My_print_js( $data /* Take the argument man! */ ) {
   echo '<script>';
   echo 'dlayer.push('.json_encode($data).')'
   echo '</script>';
} 

Now for the final catch: even if you apply everything above, your code is still unlikely to work, since there's no certainty as to when the user_register action will fire - your code simply prints a <script> tag whenever it runs, with no guarantee that it's within the context of a HTML document, or that it will even print (what if there's a redirect header immediately after?).

I would suggest the following approach, and then test that it works for the scenario in which user_register fires where you need it:

function wpse_200441_user_register( $user_id ) {
    global $wpse_200441_user_register;

    // Store the user ID that just registered in a global so that the script
    // function can access it later.
    $wpse_200441_user_register = $user_id;

    // Hook the script function
    add_action( 'wp_footer', 'wpse_200441_script' );
}

add_action( 'user_register', 'wpse_200441_user_register' );

function wpse_200441_script() {
    global $wpse_200441_user_register;

    if ( ! empty( $wpse_200441_user_register ) ) {
        $json = json_encode(
            array(
                'user_id' => $wpse_200441_user_register,
            )
        );

        echo "<script>dlayer.push( $json );</script>"; 
    }
}