Subscription Form problem

Hi, I was trying to do a popup with the subscription form you give, but I want to do that when it submits the form it close the window and I try many things and I could not do it 🙁 .

Where should I put the fuction Javascript on the code for close when it submits.

Thanks

CODE:

<div class=”newsletter newsletter-subscription”>
<form method=”post” action=”http://blabla.com.es/wp-content/plugins/newsletter/do/subscribe.php&#8221; onsubmit=”return newsletter_check(this)”>

I try: onsubmit=”return newsletter_check(this); window.close();”

Or

onsubmit= window.close();”

And still not working, thanks!

https://wordpress.org/plugins/newsletter/