Submit the form closest to a button.

submit-closest-form.js

/*
 *  A jQuery alternative to providing a custom ID selector to submit a form 
 *  is to submit the form closest to the button that has been clicked.
 *  See http://api.jquery.com/closest/
 */

$('.js-btn-submit').on('click', function(e) {
    e.preventDefault();
    $(this).closest('form').submit();
});