Insert an external library to your drupal7 theme #mmenu

mmenu-responsive.js

// We should add our js definition into our theme's js folder.

/**
 * @file
 * A JavaScript file for the Main Menu Responsive behaviour.
 */

(function ($, Drupal, window, document, undefined) {
    "use strict";
    // Reset ww value.
    var ww = null;

    Drupal.behaviors.fvfZenMaimenuResponsive= {
        attach: function(context, settings) {

            ww = document.body.clientWidth;
            startMmenu();

            // Check on resize page.
            $(window).bind('resize orientationchange', function() {
                ww = document.body.clientWidth;
                startMmenu();
            });
        }
    };

    /**
     * Start Mmenu element for left sliding Main menu only on mobile.
     */
    var startMmenu = function() {
        var mbreakpoint = 736;

        if ((ww < mbreakpoint) && (!$('.mm-page').length) ) {
            $('#navigation').mmenu({
                slidingSubmenus: false,
                isMenu: true,
            }, {
                listClass: 'menu',
            });
            $("#navigation-open").bind('click', function(e) {
                e.preventDefault();
                $("#navigation").trigger("open.mm");
            });
            $("#navigation-close").bind('click', function(e) {
                e.preventDefault();
                $("#navigation").trigger("close.mm");
            });
        }
        else if (ww >= mbreakpoint && $('.mm-page').length ) {
            $('#navigation').appendTo('#header .header__content').removeClass('mm-menu mm-vertical mm-offcanvas');
        }
        else if ((ww < mbreakpoint) && $('.mm-page').length) {
            $('#navigation').prependTo('body').addClass('mm-menu mm-vertical mm-offcanvas');
        }
    }

})(jQuery, Drupal, this, this.document);

template.php

<?php
/**
 * @file
 * Contains the theme's functions to manipulate Drupal's default markup.
 *
 * Complete documentation for this file is available online.
 * @see https://drupal.org/node/1728096
 */
 
function yourtheme_preprocess_html(&$variables, $hook) {
  drupal_add_library('yourmodule', 'mmenu');
  drupal_add_js(drupal_get_path('theme', 'yourtheme') . '/js/mainmenu-responsive.js', 'file');
}

yourmodule.module.php

<?php
/**
 * Implements hook_library().
 */
function yourmodule_library() {
  // Declares mmenu library.
  $libraries['mmenu'] = array(
    'title' => 'mmenu',
    'website' => 'http://mmenu.frebsite.nl',
    'version' => '4.5',
    'js' => array(
      libraries_get_path('mmenu') . '/src/js/jquery.mmenu.min.js' => array(),
    ),
    'css' => array(
      libraries_get_path('mmenu') . '/src/css/jquery.mmenu.css' => array(
        'type' => 'file',
        'media' => 'screen',
      ),
    ),
  );
  return $libraries;
}