jQuery plugin で submit イベント2つを両立する

HTML

<form>
  <p><label>名前<input name="name" type="text" required /></label></p>
  <input type="submit" value="submit">
</form>

<ul>
 <li><a href="https://teratail.com/questions/27111">jQueryに関する質問です。(27111)｜teratail</a></li>
</ul>

JavaScript

'use strict';
/**
 * plugin-A
 **/
jQuery.fn.setValidateForm = (function (jQuery, handleSubmit, handleInvalid) {
  return function setValidateForm () {
    for (var i = 0, l = this.length, form; i < l; ++i) {
      form = this[i];

      if (form.tagName === 'FORM') {
        jQuery(form).on('submit', handleSubmit);

        for (var j = 0, elements = form.elements, m = elements.length, element, errMsg; j < m; ++j) {
          element = elements[j];

          if (element.willValidate) {
            jQuery(element).on('invalid', handleInvalid);
          }
        }
      }
    }

    return this;
  }
}(jQuery, function handleSubmit (event) {
  var form = event.target;

  if (!form.checkValidity()) {
    event.stopPropagation();
    event.preventDefault();
  }
},
function handleInvalid (event) {
  var element = event.target,
      validity = element.validity;

  if (validity.valueMissing && element.required) {
    element.setCustomValidity('必須項目です(カスタムエラーメッセージ)');
  }
}));

/**
 * plugin-B
 **/
jQuery.fn.setConfirmSubmitForm = (function (jQuery, handleSubmit) {
  return function setConfirmSubmitForm () {
    for (var i = 0, l = this.length, form; i < l; ++i) {
      form = this[i];

      if (form.tagName === 'FORM') {
        jQuery(form).on('submit', handleSubmit);
      }
    }

    return this;
  };
}(jQuery, function handleSubmit (event) {
  var form = event.target,
      window = form.ownerDocument.defaultView;

  if (!window.confirm('送信しますか？')) {
    event.preventDefault();
  }
}));

jQuery('form').setValidateForm().setConfirmSubmitForm();