xbase-2.x-dev/js/libraries/jquery.scrolltotop.js

;(function($, window, document, undefined) {
	'use strict';

  var pluginName = 'scrollToTop';
  var defaults = {
    showAfterScrollTop: 0,
    visibleClass: 'scroll-to-top--visible'
  };

  function Plugin(element, options) {
    this.element = element;
    this.settings = $.extend({}, defaults, options);
    this._defaults = defaults;
    this._name = pluginName;
    this.init();
  }

  $.extend(Plugin.prototype, {
    /**
     * Plugin init.
     */
    init: function() {
      var pluginInstance = this;
      var $element = $(pluginInstance.element);

      $element.on('click', function (event) {
        window.scrollTo({
          top: 0,
          behavior: 'smooth',
        });
        event.preventDefault();
      });

      var scrollTimer;
      $(document).on('scroll', function () {
        if (scrollTimer) {
          clearTimeout(scrollTimer);
        }
        scrollTimer = setTimeout(function() {
          pluginInstance.check();
        }, 20);
      });
      pluginInstance.check();
    },

    /**
     * Show/hide element.
     */
    check: function () {
      var pluginInstance = this;
      var $element = $(pluginInstance.element);
      var viewportHeight = $(window).height();
      var windowScrollTop = $(window).scrollTop();

      // Show
      if (windowScrollTop > this.settings.showAfterScrollTop) {
        if (!$element.hasClass(this.settings.visibleClass)) {
          $element.addClass(this.settings.visibleClass);
        }
      }
      // Hide
      else {
        if ($element.hasClass(this.settings.visibleClass)) {
          $element.removeClass(this.settings.visibleClass);
        }
      }
    },
  });

  $.fn[pluginName] = function (options) {
    return this.each(function () {
      if (!$.data(this, 'plugin_' + pluginName)) {
        $.data(this, 'plugin_' + pluginName, new Plugin(this, options));
      }
    });
  };

})(jQuery, window, document);