"Cannot read property classList" null "when using classList.add

I have this error, but since I am not familiar with the code. This came from a theme in startbootstrap (Creative). File

classie.js

code:

/*!
 * classie - class helper functions
 * from bonzo https://github.com/ded/bonzo
 * 
 * classie.has( elem, 'my-class' ) -> true/false
 * classie.add( elem, 'my-new-class' )
 * classie.remove( elem, 'my-unwanted-class' )
 * classie.toggle( elem, 'my-class' )
 */

/*jshint browser: true, strict: true, undef: true */
/*global define: false */

( function( window ) {

'use strict';

// class helper functions from bonzo https://github.com/ded/bonzo

function classReg( className ) {
  return new RegExp("(^|\\s+)" + className + "(\\s+|$)");
}

// classList support for class management
// altho to be fair, the api sucks because it won't accept multiple classes at once
var hasClass, addClass, removeClass;

if ( 'classList' in document.documentElement ) {
  hasClass = function( elem, c ) {
    return elem.classList.contains( c );
  };
  addClass = function( elem, c ) {
    elem.classList.add( c );
  };
  removeClass = function( elem, c ) {
    elem.classList.remove( c );
  };
}
else {
  hasClass = function( elem, c ) {
    return classReg( c ).test( elem.className );
  };
  addClass = function( elem, c ) {
    if ( !hasClass( elem, c ) ) {
      elem.className = elem.className + ' ' + c;
    }
  };
  removeClass = function( elem, c ) {
    elem.className = elem.className.replace( classReg( c ), ' ' );
  };
}

function toggleClass( elem, c ) {
  var fn = hasClass( elem, c ) ? removeClass : addClass;
  fn( elem, c );
}

var classie = {
  // full names
  hasClass: hasClass,
  addClass: addClass,
  removeClass: removeClass,
  toggleClass: toggleClass,
  // short names
  has: hasClass,
  add: addClass,
  remove: removeClass,
  toggle: toggleClass
};

// transport
if ( typeof define === 'function' && define.amd ) {
  // AMD
  define( classie );
} else {
  // browser global
  window.classie = classie;
}

})( window );

      

        
        
        
      

    

the error is in:

elem.classList.add (c);

I am not familiar with the written code. I am including this file along with other js files. And it seems like another js file needs a classie variable .

Editorial staff:

HERE IS AN ERROR IN THE CONSOLE:

Uncaught TypeError: Cannot read property 'classList' of null
  addClass @ classie.js?nngrmm:33
  scrollPage @ cbpAnimatedHeader.js?nngrmm:30

      

        
        
        
      

    

ALSO, I have a bug in bootstrap.js.

Uncaught TypeError: $(...).find(...).once is not a function
  Drupal.behaviors.bootstrap.attach @ bootstrap.js?nngrmm:16
  (anonymous function) @ drupal.js?nngrmm:76
  x.extend.each @ jquery.min.js?v=1.10.2:4
  Drupal.attachBehaviors @ drupal.js?nngrmm:74
  (anonymous function) @ drupal.js?nngrmm:412
  x.Callbacks.c @ jquery.min.js?v=1.10.2:4
  x.Callbacks.p.fireWith @ jquery.min.js?v=1.10.2:4
  x.extend.ready @ jquery.min.js?v=1.10.2:4
  q @ jquery.min.js?v=1.10.2:4

      

        
        
        
      

    

Somewhere here:

/**
 * @file
 * bootstrap.js
 *
 * Provides general enhancements and fixes to Bootstrap JS files.
 */

var Drupal = Drupal || {};

(function($, Drupal){
  "use strict";

  Drupal.behaviors.bootstrap = {
    attach: function(context) {
      // Provide some Bootstrap tab/Drupal integration.
      $(context).find('.tabbable').once('bootstrap-tabs', function () {
        var $wrapper = $(this);
        var $tabs = $wrapper.find('.nav-tabs');
        var $content = $wrapper.find('.tab-content');
        var borderRadius = parseInt($content.css('borderBottomRightRadius'), 10);
        var bootstrapTabResize = function() {
          if ($wrapper.hasClass('tabs-left') || $wrapper.hasClass('tabs-right')) {
            $content.css('min-height', $tabs.outerHeight());
          }
        };
        // Add min-height on content for left and right tabs.
        bootstrapTabResize();
        // Detect tab switch.
        if ($wrapper.hasClass('tabs-left') || $wrapper.hasClass('tabs-right')) {
          $tabs.on('shown.bs.tab', 'a[data-toggle="tab"]', function (e) {
            bootstrapTabResize();
            if ($wrapper.hasClass('tabs-left')) {
              if ($(e.target).parent().is(':first-child')) {
                $content.css('borderTopLeftRadius', '0');
              }
              else {
                $content.css('borderTopLeftRadius', borderRadius + 'px');
              }
            }
            else {
              if ($(e.target).parent().is(':first-child')) {
                $content.css('borderTopRightRadius', '0');
              }
              else {
                $content.css('borderTopRightRadius', borderRadius + 'px');
              }
            }
          });
        }
      });
    }
  };

      

        
        
        
      

    

Mistake:

$ (context) .find ('. tabbable'). once ('bootstrap-tabs', function () {

Help is needed. Thank.