enewsletter placeholder

I placed the enewsletter signup widget in the footer of my site and another one in a bar using the do_shortcode() function. They both work fine.
I wanted to add a placeholder to the email field of both of them, I read the instructions of this post (link) but the placeholder is shown only in one of the two email field.
and used this code

function wpmu_enewsletter_form_placeholder() {
    <script type="text/javascript">
    jQuery(function($) {
         $('#e_newsletter_email').attr("placeholder", "Your email address");
add_action('wp_footer', 'wpmu_enewsletter_form_placeholder');

How can I do to have both field with the placeholder? thank you