block form double-submission

preventDoubleSubmission.js

// jQuery plugin to prevent double submission of forms
jQuery.fn.preventDoubleSubmission = function() {
  $(this).on('submit',function(e){
    var $form = $(this);
 
    if ($form.data('submitted') === true) {
      // don't submit
      e.preventDefault();
    } else {
      // set data attr to true for next time
      $form.data('submitted', true);
    }
  });
 
  // Keep chainability
  return this;
};