mixpanel-core.js

/* eslint camelcase: "off" */
import Config from './config';
import { MAX_RECORDING_MS, _, console, userAgent, document, navigator, slice, NOOP_FUNC, JSONStringify } from './utils';
import { isRecordingExpired } from './recorder/utils';
import { window } from './window';
import { Autocapture } from './autocapture';
import { FeatureFlagManager } from './flags';
import { FormTracker, LinkTracker } from './dom-trackers';
import { RequestBatcher } from './request-batcher';
import { MixpanelGroup } from './mixpanel-group';
import { MixpanelPeople } from './mixpanel-people';
import {
    MixpanelPersistence,
    PEOPLE_DISTINCT_ID_KEY,
    ALIAS_ID_KEY
} from './mixpanel-persistence';
import {
    optIn,
    optOut,
    hasOptedIn,
    hasOptedOut,
    clearOptInOut,
    addOptOutCheckMixpanelLib
} from './gdpr-utils';
import { IDBStorageWrapper, RECORDING_REGISTRY_STORE_NAME } from './storage/indexed-db';

/*
 * Mixpanel JS Library
 *
 * Copyright 2012, Mixpanel, Inc. All Rights Reserved
 * http://mixpanel.com/
 *
 * Includes portions of Underscore.js
 * http://documentcloud.github.com/underscore/
 * (c) 2011 Jeremy Ashkenas, DocumentCloud Inc.
 * Released under the MIT License.
 */

/*
SIMPLE STYLE GUIDE:

this.x === public function
this._x === internal - only use within this file
this.__x === private - only use within the class

Globals should be all caps
*/

var init_type;       // MODULE or SNIPPET loader
// allow bundlers to specify how extra code (recorder bundle) should be loaded
// eslint-disable-next-line no-unused-vars
var load_extra_bundle = function(src, _onload) {
    throw new Error(src + ' not available in this build.');
};

var mixpanel_master; // main mixpanel instance / object
var INIT_MODULE  = 0;
var INIT_SNIPPET = 1;

var IDENTITY_FUNC = function(x) {return x;};

/** @const */ var PRIMARY_INSTANCE_NAME = 'mixpanel';
/** @const */ var PAYLOAD_TYPE_BASE64   = 'base64';
/** @const */ var PAYLOAD_TYPE_JSON     = 'json';
/** @const */ var DEVICE_ID_PREFIX      = '$device:';


/*
 * Dynamic... constants? Is that an oxymoron?
 */
// http://hacks.mozilla.org/2009/07/cross-site-xmlhttprequest-with-cors/
// https://developer.mozilla.org/en-US/docs/DOM/XMLHttpRequest#withCredentials
var USE_XHR = (window.XMLHttpRequest && 'withCredentials' in new XMLHttpRequest());

// IE<10 does not support cross-origin XHR's but script tags
// with defer won't block window.onload; ENQUEUE_REQUESTS
// should only be true for Opera<12
var ENQUEUE_REQUESTS = !USE_XHR && (userAgent.indexOf('MSIE') === -1) && (userAgent.indexOf('Mozilla') === -1);

// save reference to navigator.sendBeacon so it can be minified
var sendBeacon = null;
if (navigator['sendBeacon']) {
    sendBeacon = function() {
        // late reference to navigator.sendBeacon to allow patching/spying
        return navigator['sendBeacon'].apply(navigator, arguments);
    };
}

var DEFAULT_API_ROUTES = {
    'track':  'track/',
    'engage': 'engage/',
    'groups': 'groups/',
    'record': 'record/',
    'flags':  'flags/'
};

/*
 * Module-level globals
 */
var DEFAULT_CONFIG = {
    'api_host':                          'https://api-js.mixpanel.com',
    'api_routes':                        DEFAULT_API_ROUTES,
    'api_method':                        'POST',
    'api_transport':                     'XHR',
    'api_payload_format':                PAYLOAD_TYPE_BASE64,
    'app_host':                          'https://mixpanel.com',
    'autocapture':                       false,
    'cdn':                               'https://cdn.mxpnl.com',
    'cross_site_cookie':                 false,
    'cross_subdomain_cookie':            true,
    'error_reporter':                    NOOP_FUNC,
    'flags':                             false,
    'persistence':                       'cookie',
    'persistence_name':                  '',
    'cookie_domain':                     '',
    'cookie_name':                       '',
    'loaded':                            NOOP_FUNC,
    'mp_loader':                         null,
    'track_marketing':                   true,
    'track_pageview':                    false,
    'skip_first_touch_marketing':        false,
    'store_google':                      true,
    'stop_utm_persistence':              false,
    'save_referrer':                     true,
    'test':                              false,
    'verbose':                           false,
    'img':                               false,
    'debug':                             false,
    'track_links_timeout':               300,
    'cookie_expiration':                 365,
    'upgrade':                           false,
    'disable_persistence':               false,
    'disable_cookie':                    false,
    'secure_cookie':                     false,
    'ip':                                true,
    'opt_out_tracking_by_default':       false,
    'opt_out_persistence_by_default':    false,
    'opt_out_tracking_persistence_type': 'localStorage',
    'opt_out_tracking_cookie_prefix':    null,
    'property_blacklist':                [],
    'xhr_headers':                       {}, // { header: value, header2: value }
    'ignore_dnt':                        false,
    'batch_requests':                    true,
    'batch_size':                        50,
    'batch_flush_interval_ms':           5000,
    'batch_request_timeout_ms':          90000,
    'batch_autostart':                   true,
    'hooks':                             {},
    'record_block_class':                new RegExp('^(mp-block|fs-exclude|amp-block|rr-block|ph-no-capture)$'),
    'record_block_selector':             'img, video',
    'record_canvas':                     false,
    'record_collect_fonts':              false,
    'record_heatmap_data':               false,
    'record_idle_timeout_ms':            30 * 60 * 1000, // 30 minutes
    'record_mask_text_class':            new RegExp('^(mp-mask|fs-mask|amp-mask|rr-mask|ph-mask)$'),
    'record_mask_text_selector':         '*',
    'record_max_ms':                     MAX_RECORDING_MS,
    'record_min_ms':                     0,
    'record_sessions_percent':           0,
    'recorder_src':                      'https://cdn.mxpnl.com/libs/mixpanel-recorder.min.js'
};

var DOM_LOADED = false;

/**
 * Mixpanel Library Object
 * @constructor
 */
var MixpanelLib = function() {};


/**
 * create_mplib(token:string, config:object, name:string)
 *
 * This function is used by the init method of MixpanelLib objects
 * as well as the main initializer at the end of the JSLib (that
 * initializes document.mixpanel as well as any additional instances
 * declared before this file has loaded).
 */
var create_mplib = function(token, config, name) {
    var instance,
        target = (name === PRIMARY_INSTANCE_NAME) ? mixpanel_master : mixpanel_master[name];

    if (target && init_type === INIT_MODULE) {
        instance = target;
    } else {
        if (target && !_.isArray(target)) {
            console.error('You have already initialized ' + name);
            return;
        }
        instance = new MixpanelLib();
    }

    instance._cached_groups = {}; // cache groups in a pool

    instance._init(token, config, name);

    instance['people'] = new MixpanelPeople();
    instance['people']._init(instance);

    if (!instance.get_config('skip_first_touch_marketing')) {
        // We need null UTM params in the object because
        // UTM parameters act as a tuple. If any UTM param
        // is present, then we set all UTM params including
        // empty ones together
        var utm_params = _.info.campaignParams(null);
        var initial_utm_params = {};
        var has_utm = false;
        _.each(utm_params, function(utm_value, utm_key) {
            initial_utm_params['initial_' + utm_key] = utm_value;
            if (utm_value) {
                has_utm = true;
            }
        });
        if (has_utm) {
            instance['people'].set_once(initial_utm_params);
        }
    }

    // if any instance on the page has debug = true, we set the
    // global debug to be true
    Config.DEBUG = Config.DEBUG || instance.get_config('debug');

    // if target is not defined, we called init after the lib already
    // loaded, so there won't be an array of things to execute
    if (!_.isUndefined(target) && _.isArray(target)) {
        // Crunch through the people queue first - we queue this data up &
        // flush on identify, so it's better to do all these operations first
        instance._execute_array.call(instance['people'], target['people']);
        instance._execute_array(target);
    }

    return instance;
};

// Initialization methods

/**
 * This function initializes a new instance of the Mixpanel tracking object.
 * All new instances are added to the main mixpanel object as sub properties (such as
 * mixpanel.library_name) and also returned by this function. To define a
 * second instance on the page, you would call:
 *
 *     mixpanel.init('new token', { your: 'config' }, 'library_name');
 *
 * and use it like so:
 *
 *     mixpanel.library_name.track(...);
 *
 * @param {String} token   Your Mixpanel API token
 * @param {Object} [config]  A dictionary of config options to override. <a href="https://github.com/mixpanel/mixpanel-js/blob/v2.46.0/src/mixpanel-core.js#L88-L127">See a list of default config options</a>.
 * @param {String} [name]    The name for the new mixpanel instance that you want created
 */
MixpanelLib.prototype.init = function (token, config, name) {
    if (_.isUndefined(name)) {
        this.report_error('You must name your new library: init(token, config, name)');
        return;
    }
    if (name === PRIMARY_INSTANCE_NAME) {
        this.report_error('You must initialize the main mixpanel object right after you include the Mixpanel js snippet');
        return;
    }

    var instance = create_mplib(token, config, name);
    mixpanel_master[name] = instance;
    instance._loaded();

    return instance;
};

// mixpanel._init(token:string, config:object, name:string)
//
// This function sets up the current instance of the mixpanel
// library.  The difference between this method and the init(...)
// method is this one initializes the actual instance, whereas the
// init(...) method sets up a new library and calls _init on it.
//
MixpanelLib.prototype._init = function(token, config, name) {
    config = config || {};

    this['__loaded'] = true;
    this['config'] = {};

    var variable_features = {};

    // default to JSON payload for standard mixpanel.com API hosts
    if (!('api_payload_format' in config)) {
        var api_host = config['api_host'] || DEFAULT_CONFIG['api_host'];
        if (api_host.match(/\.mixpanel\.com/)) {
            variable_features['api_payload_format'] = PAYLOAD_TYPE_JSON;
        }
    }

    this.set_config(_.extend({}, DEFAULT_CONFIG, variable_features, config, {
        'name': name,
        'token': token,
        'callback_fn': ((name === PRIMARY_INSTANCE_NAME) ? name : PRIMARY_INSTANCE_NAME + '.' + name) + '._jsc'
    }));

    this['_jsc'] = NOOP_FUNC;

    this.__dom_loaded_queue = [];
    this.__request_queue = [];
    this.__disabled_events = [];
    this._flags = {
        'disable_all_events': false,
        'identify_called': false
    };

    // set up request queueing/batching
    this.request_batchers = {};
    this._batch_requests = this.get_config('batch_requests');
    if (this._batch_requests) {
        if (!_.localStorage.is_supported(true) || !USE_XHR) {
            this._batch_requests = false;
            console.log('Turning off Mixpanel request-queueing; needs XHR and localStorage support');
            _.each(this.get_batcher_configs(), function(batcher_config) {
                console.log('Clearing batch queue ' + batcher_config.queue_key);
                _.localStorage.remove(batcher_config.queue_key);
            });
        } else {
            this.init_batchers();
            if (sendBeacon && window.addEventListener) {
                // Before page closes or hides (user tabs away etc), attempt to flush any events
                // queued up via navigator.sendBeacon. Since sendBeacon doesn't report success/failure,
                // events will not be removed from the persistent store; if the site is loaded again,
                // the events will be flushed again on startup and deduplicated on the Mixpanel server
                // side.
                // There is no reliable way to capture only page close events, so we lean on the
                // visibilitychange and pagehide events as recommended at
                // https://developer.mozilla.org/en-US/docs/Web/API/Window/unload_event#usage_notes.
                // These events fire when the user clicks away from the current page/tab, so will occur
                // more frequently than page unload, but are the only mechanism currently for capturing
                // this scenario somewhat reliably.
                var flush_on_unload = _.bind(function() {
                    if (!this.request_batchers.events.stopped) {
                        this.request_batchers.events.flush({unloading: true});
                    }
                }, this);
                window.addEventListener('pagehide', function(ev) {
                    if (ev['persisted']) {
                        flush_on_unload();
                    }
                });
                window.addEventListener('visibilitychange', function() {
                    if (document['visibilityState'] === 'hidden') {
                        flush_on_unload();
                    }
                });
            }
        }
    }

    this['persistence'] = this['cookie'] = new MixpanelPersistence(this['config']);
    this.unpersisted_superprops = {};
    this._gdpr_init();

    var uuid = _.UUID();
    if (!this.get_distinct_id()) {
        // There is no need to set the distinct id
        // or the device id if something was already stored
        // in the persitence
        this.register_once({
            'distinct_id': DEVICE_ID_PREFIX + uuid,
            '$device_id': uuid
        }, '');
    }

    this.flags = new FeatureFlagManager({
        getConfigFunc: _.bind(this.get_config, this),
        getDistinctIdFunc: _.bind(this.get_distinct_id, this),
        trackingFunc: _.bind(this.track, this)
    });
    this.flags.init();
    this['flags'] = this.flags;

    this.autocapture = new Autocapture(this);
    this.autocapture.init();

    this._init_tab_id();
    this._check_and_start_session_recording();
};

/**
 * Assigns a unique UUID to this tab / window by leveraging sessionStorage.
 * This is primarily used for session recording, where data must be isolated to the current tab.
 */
MixpanelLib.prototype._init_tab_id = function() {
    if (_.sessionStorage.is_supported()) {
        try {
            var key_suffix = this.get_config('name') + '_' + this.get_config('token');
            var tab_id_key = 'mp_tab_id_' + key_suffix;

            // A flag is used to determine if sessionStorage is copied over and we need to generate a new tab ID.
            // This enforces a unique ID in the cases like duplicated tab, window.open(...)
            var should_generate_new_tab_id_key = 'mp_gen_new_tab_id_' + key_suffix;
            if (_.sessionStorage.get(should_generate_new_tab_id_key) || !_.sessionStorage.get(tab_id_key)) {
                _.sessionStorage.set(tab_id_key, '$tab-' + _.UUID());
            }

            _.sessionStorage.set(should_generate_new_tab_id_key, '1');
            this.tab_id = _.sessionStorage.get(tab_id_key);

            // Remove the flag when the tab is unloaded to indicate the stored tab ID can be reused. This event is not reliable to detect all page unloads,
            // but reliable in cases where the user remains in the tab e.g. a refresh or href navigation.
            // If the flag is absent, this indicates to the next SDK instance that we can reuse the stored tab_id.
            window.addEventListener('beforeunload', function () {
                _.sessionStorage.remove(should_generate_new_tab_id_key);
            });
        } catch(err) {
            this.report_error('Error initializing tab id', err);
        }
    } else {
        this.report_error('Session storage is not supported, cannot keep track of unique tab ID.');
    }
};

MixpanelLib.prototype.get_tab_id = function () {
    return this.tab_id || null;
};

MixpanelLib.prototype._should_load_recorder = function () {
    var recording_registry_idb = new IDBStorageWrapper(RECORDING_REGISTRY_STORE_NAME);
    var tab_id = this.get_tab_id();
    return recording_registry_idb.init()
        .then(function () {
            return recording_registry_idb.getAll();
        })
        .then(function (recordings) {
            for (var i = 0; i < recordings.length; i++) {
                // if there are expired recordings in the registry, we should load the recorder to flush them
                // if there's a recording for this tab id, we should load the recorder to continue the recording
                if (isRecordingExpired(recordings[i]) || recordings[i]['tabId'] === tab_id) {
                    return true;
                }
            }
            return false;
        })
        .catch(_.bind(function (err) {
            this.report_error('Error checking recording registry', err);
        }, this));
};

MixpanelLib.prototype._check_and_start_session_recording = addOptOutCheckMixpanelLib(function(force_start) {
    if (!window['MutationObserver']) {
        console.critical('Browser does not support MutationObserver; skipping session recording');
        return;
    }

    var loadRecorder = _.bind(function(startNewIfInactive) {
        var handleLoadedRecorder = _.bind(function() {
            this._recorder = this._recorder || new window['__mp_recorder'](this);
            this._recorder['resumeRecording'](startNewIfInactive);
        }, this);

        if (_.isUndefined(window['__mp_recorder'])) {
            load_extra_bundle(this.get_config('recorder_src'), handleLoadedRecorder);
        } else {
            handleLoadedRecorder();
        }
    }, this);

    /**
     * If the user is sampled or start_session_recording is called, we always load the recorder since it's guaranteed a recording should start.
     * Otherwise, if the recording registry has any records then it's likely there's a recording in progress or orphaned data that needs to be flushed.
     */
    var is_sampled = this.get_config('record_sessions_percent') > 0 && Math.random() * 100 <= this.get_config('record_sessions_percent');
    if (force_start || is_sampled) {
        loadRecorder(true);
    } else {
        this._should_load_recorder()
            .then(function (shouldLoad) {
                if (shouldLoad) {
                    loadRecorder(false);
                }
            });
    }
});

MixpanelLib.prototype.start_session_recording = function () {
    this._check_and_start_session_recording(true);
};

MixpanelLib.prototype.stop_session_recording = function () {
    if (this._recorder) {
        this._recorder['stopRecording']();
    }
};

MixpanelLib.prototype.pause_session_recording = function () {
    if (this._recorder) {
        this._recorder['pauseRecording']();
    }
};

MixpanelLib.prototype.resume_session_recording = function () {
    if (this._recorder) {
        this._recorder['resumeRecording']();
    }
};

MixpanelLib.prototype.is_recording_heatmap_data = function () {
    return this._get_session_replay_id() && this.get_config('record_heatmap_data');
};

MixpanelLib.prototype.get_session_recording_properties = function () {
    var props = {};
    var replay_id = this._get_session_replay_id();
    if (replay_id) {
        props['$mp_replay_id'] = replay_id;
    }
    return props;
};

MixpanelLib.prototype.get_session_replay_url = function () {
    var replay_url = null;
    var replay_id = this._get_session_replay_id();
    if (replay_id) {
        var query_params = _.HTTPBuildQuery({
            'replay_id': replay_id,
            'distinct_id': this.get_distinct_id(),
            'token': this.get_config('token')
        });
        replay_url = 'https://mixpanel.com/projects/replay-redirect?' + query_params;
    }
    return replay_url;
};

MixpanelLib.prototype._get_session_replay_id = function () {
    var replay_id = null;
    if (this._recorder) {
        replay_id = this._recorder['replayId'];
    }
    return replay_id || null;
};

// "private" public method to reach into the recorder in test cases
MixpanelLib.prototype.__get_recorder = function () {
    return this._recorder;
};

// Private methods

MixpanelLib.prototype._loaded = function() {
    this.get_config('loaded')(this);
    this._set_default_superprops();
    this['people'].set_once(this['persistence'].get_referrer_info());

    // `store_google` is now deprecated and previously stored UTM parameters are cleared
    // from persistence by default.
    if (this.get_config('store_google') && this.get_config('stop_utm_persistence')) {
        var utm_params = _.info.campaignParams(null);
        _.each(utm_params, function(_utm_value, utm_key) {
            // We need to unregister persisted UTM parameters so old values
            // are not mixed with the new UTM parameters
            this.unregister(utm_key);
        }.bind(this));
    }
};

// update persistence with info on referrer, UTM params, etc
MixpanelLib.prototype._set_default_superprops = function() {
    this['persistence'].update_search_keyword(document.referrer);
    // Registering super properties for UTM persistence by 'store_google' is deprecated.
    if (this.get_config('store_google') && !this.get_config('stop_utm_persistence')) {
        this.register(_.info.campaignParams());
    }
    if (this.get_config('save_referrer')) {
        this['persistence'].update_referrer_info(document.referrer);
    }
};

MixpanelLib.prototype._dom_loaded = function() {
    _.each(this.__dom_loaded_queue, function(item) {
        this._track_dom.apply(this, item);
    }, this);

    if (!this.has_opted_out_tracking()) {
        _.each(this.__request_queue, function(item) {
            this._send_request.apply(this, item);
        }, this);
    }

    delete this.__dom_loaded_queue;
    delete this.__request_queue;
};

MixpanelLib.prototype._track_dom = function(DomClass, args) {
    if (this.get_config('img')) {
        this.report_error('You can\'t use DOM tracking functions with img = true.');
        return false;
    }

    if (!DOM_LOADED) {
        this.__dom_loaded_queue.push([DomClass, args]);
        return false;
    }

    var dt = new DomClass().init(this);
    return dt.track.apply(dt, args);
};

/**
 * _prepare_callback() should be called by callers of _send_request for use
 * as the callback argument.
 *
 * If there is no callback, this returns null.
 * If we are going to make XHR/XDR requests, this returns a function.
 * If we are going to use script tags, this returns a string to use as the
 * callback GET param.
 */
MixpanelLib.prototype._prepare_callback = function(callback, data) {
    if (_.isUndefined(callback)) {
        return null;
    }

    if (USE_XHR) {
        var callback_function = function(response) {
            callback(response, data);
        };
        return callback_function;
    } else {
        // if the user gives us a callback, we store as a random
        // property on this instances jsc function and update our
        // callback string to reflect that.
        var jsc = this['_jsc'];
        var randomized_cb = '' + Math.floor(Math.random() * 100000000);
        var callback_string = this.get_config('callback_fn') + '[' + randomized_cb + ']';
        jsc[randomized_cb] = function(response) {
            delete jsc[randomized_cb];
            callback(response, data);
        };
        return callback_string;
    }
};

MixpanelLib.prototype._send_request = function(url, data, options, callback) {
    var succeeded = true;

    if (ENQUEUE_REQUESTS) {
        this.__request_queue.push(arguments);
        return succeeded;
    }

    var DEFAULT_OPTIONS = {
        method: this.get_config('api_method'),
        transport: this.get_config('api_transport'),
        verbose: this.get_config('verbose')
    };
    var body_data = null;

    if (!callback && (_.isFunction(options) || typeof options === 'string')) {
        callback = options;
        options = null;
    }
    options = _.extend(DEFAULT_OPTIONS, options || {});
    if (!USE_XHR) {
        options.method = 'GET';
    }
    var use_post = options.method === 'POST';
    var use_sendBeacon = sendBeacon && use_post && options.transport.toLowerCase() === 'sendbeacon';

    // needed to correctly format responses
    var verbose_mode = options.verbose;
    if (data['verbose']) { verbose_mode = true; }

    if (this.get_config('test')) { data['test'] = 1; }
    if (verbose_mode) { data['verbose'] = 1; }
    if (this.get_config('img')) { data['img'] = 1; }
    if (!USE_XHR) {
        if (callback) {
            data['callback'] = callback;
        } else if (verbose_mode || this.get_config('test')) {
            // Verbose output (from verbose mode, or an error in test mode) is a json blob,
            // which by itself is not valid javascript. Without a callback, this verbose output will
            // cause an error when returned via jsonp, so we force a no-op callback param.
            // See the ECMA script spec: http://www.ecma-international.org/ecma-262/5.1/#sec-12.4
            data['callback'] = '(function(){})';
        }
    }

    data['ip'] = this.get_config('ip')?1:0;
    data['_'] = new Date().getTime().toString();

    if (use_post) {
        body_data = 'data=' + encodeURIComponent(data['data']);
        delete data['data'];
    }

    url += '?' + _.HTTPBuildQuery(data);

    var lib = this;
    if ('img' in data) {
        var img = document.createElement('img');
        img.src = url;
        document.body.appendChild(img);
    } else if (use_sendBeacon) {
        try {
            succeeded = sendBeacon(url, body_data);
        } catch (e) {
            lib.report_error(e);
            succeeded = false;
        }
        try {
            if (callback) {
                callback(succeeded ? 1 : 0);
            }
        } catch (e) {
            lib.report_error(e);
        }
    } else if (USE_XHR) {
        try {
            var req = new XMLHttpRequest();
            req.open(options.method, url, true);

            var headers = this.get_config('xhr_headers');
            if (use_post) {
                headers['Content-Type'] = 'application/x-www-form-urlencoded';
            }
            _.each(headers, function(headerValue, headerName) {
                req.setRequestHeader(headerName, headerValue);
            });

            if (options.timeout_ms && typeof req.timeout !== 'undefined') {
                req.timeout = options.timeout_ms;
                var start_time = new Date().getTime();
            }

            // send the mp_optout cookie
            // withCredentials cannot be modified until after calling .open on Android and Mobile Safari
            req.withCredentials = true;
            req.onreadystatechange = function () {
                if (req.readyState === 4) { // XMLHttpRequest.DONE == 4, except in safari 4
                    if (req.status === 200) {
                        if (callback) {
                            if (verbose_mode) {
                                var response;
                                try {
                                    response = _.JSONDecode(req.responseText);
                                } catch (e) {
                                    lib.report_error(e);
                                    if (options.ignore_json_errors) {
                                        response = req.responseText;
                                    } else {
                                        return;
                                    }
                                }
                                callback(response);
                            } else {
                                callback(Number(req.responseText));
                            }
                        }
                    } else {
                        var error;
                        if (
                            req.timeout &&
                            !req.status &&
                            new Date().getTime() - start_time >= req.timeout
                        ) {
                            error = 'timeout';
                        } else {
                            error = 'Bad HTTP status: ' + req.status + ' ' + req.statusText;
                        }
                        lib.report_error(error);
                        if (callback) {
                            if (verbose_mode) {
                                var response_headers = req['responseHeaders'] || {};
                                callback({status: 0, httpStatusCode: req['status'], error: error, retryAfter: response_headers['Retry-After']});
                            } else {
                                callback(0);
                            }
                        }
                    }
                }
            };
            req.send(body_data);
        } catch (e) {
            lib.report_error(e);
            succeeded = false;
        }
    } else {
        var script = document.createElement('script');
        script.type = 'text/javascript';
        script.async = true;
        script.defer = true;
        script.src = url;
        var s = document.getElementsByTagName('script')[0];
        s.parentNode.insertBefore(script, s);
    }

    return succeeded;
};

/**
 * _execute_array() deals with processing any mixpanel function
 * calls that were called before the Mixpanel library were loaded
 * (and are thus stored in an array so they can be called later)
 *
 * Note: we fire off all the mixpanel function calls && user defined
 * functions BEFORE we fire off mixpanel tracking calls. This is so
 * identify/register/set_config calls can properly modify early
 * tracking calls.
 *
 * @param {Array} array
 */
MixpanelLib.prototype._execute_array = function(array) {
    var fn_name, alias_calls = [], other_calls = [], tracking_calls = [];
    _.each(array, function(item) {
        if (item) {
            fn_name = item[0];
            if (_.isArray(fn_name)) {
                tracking_calls.push(item); // chained call e.g. mixpanel.get_group().set()
            } else if (typeof(item) === 'function') {
                item.call(this);
            } else if (_.isArray(item) && fn_name === 'alias') {
                alias_calls.push(item);
            } else if (_.isArray(item) && fn_name.indexOf('track') !== -1 && typeof(this[fn_name]) === 'function') {
                tracking_calls.push(item);
            } else {
                other_calls.push(item);
            }
        }
    }, this);

    var execute = function(calls, context) {
        _.each(calls, function(item) {
            if (_.isArray(item[0])) {
                // chained call
                var caller = context;
                _.each(item, function(call) {
                    caller = caller[call[0]].apply(caller, call.slice(1));
                });
            } else {
                this[item[0]].apply(this, item.slice(1));
            }
        }, context);
    };

    execute(alias_calls, this);
    execute(other_calls, this);
    execute(tracking_calls, this);
};

// request queueing utils

MixpanelLib.prototype.are_batchers_initialized = function() {
    return !!this.request_batchers.events;
};

MixpanelLib.prototype.get_batcher_configs = function() {
    var queue_prefix = '__mpq_' + this.get_config('token');
    var api_routes = this.get_config('api_routes');
    this._batcher_configs = this._batcher_configs || {
        events: {type: 'events', endpoint: '/' + api_routes['track'], queue_key: queue_prefix + '_ev'},
        people: {type: 'people', endpoint: '/' + api_routes['engage'], queue_key: queue_prefix + '_pp'},
        groups: {type: 'groups', endpoint: '/' + api_routes['groups'], queue_key: queue_prefix + '_gr'}
    };
    return this._batcher_configs;
};

MixpanelLib.prototype.init_batchers = function() {
    if (!this.are_batchers_initialized()) {
        var batcher_for = _.bind(function(attrs) {
            return new RequestBatcher(
                attrs.queue_key,
                {
                    libConfig: this['config'],
                    errorReporter: this.get_config('error_reporter'),
                    sendRequestFunc: _.bind(function(data, options, cb) {
                        this._send_request(
                            this.get_config('api_host') + attrs.endpoint,
                            this._encode_data_for_request(data),
                            options,
                            this._prepare_callback(cb, data)
                        );
                    }, this),
                    beforeSendHook: _.bind(function(item) {
                        return this._run_hook('before_send_' + attrs.type, item);
                    }, this),
                    stopAllBatchingFunc: _.bind(this.stop_batch_senders, this),
                    usePersistence: true,
                }
            );
        }, this);
        var batcher_configs = this.get_batcher_configs();
        this.request_batchers = {
            events: batcher_for(batcher_configs.events),
            people: batcher_for(batcher_configs.people),
            groups: batcher_for(batcher_configs.groups)
        };
    }
    if (this.get_config('batch_autostart')) {
        this.start_batch_senders();
    }
};

MixpanelLib.prototype.start_batch_senders = function() {
    this._batchers_were_started = true;
    if (this.are_batchers_initialized()) {
        this._batch_requests = true;
        _.each(this.request_batchers, function(batcher) {
            batcher.start();
        });
    }
};

MixpanelLib.prototype.stop_batch_senders = function() {
    this._batch_requests = false;
    _.each(this.request_batchers, function(batcher) {
        batcher.stop();
        batcher.clear();
    });
};

/**
 * push() keeps the standard async-array-push
 * behavior around after the lib is loaded.
 * This is only useful for external integrations that
 * do not wish to rely on our convenience methods
 * (created in the snippet).
 *
 * ### Usage:
 *     mixpanel.push(['register', { a: 'b' }]);
 *
 * @param {Array} item A [function_name, args...] array to be executed
 */
MixpanelLib.prototype.push = function(item) {
    this._execute_array([item]);
};

/**
 * Disable events on the Mixpanel object. If passed no arguments,
 * this function disables tracking of any event. If passed an
 * array of event names, those events will be disabled, but other
 * events will continue to be tracked.
 *
 * Note: this function does not stop other mixpanel functions from
 * firing, such as register() or people.set().
 *
 * @param {Array} [events] An array of event names to disable
 */
MixpanelLib.prototype.disable = function(events) {
    if (typeof(events) === 'undefined') {
        this._flags.disable_all_events = true;
    } else {
        this.__disabled_events = this.__disabled_events.concat(events);
    }
};

MixpanelLib.prototype._encode_data_for_request = function(data) {
    var encoded_data = JSONStringify(data);
    if (this.get_config('api_payload_format') === PAYLOAD_TYPE_BASE64) {
        encoded_data = _.base64Encode(encoded_data);
    }
    return {'data': encoded_data};
};

// internal method for handling track vs batch-enqueue logic
MixpanelLib.prototype._track_or_batch = function(options, callback) {
    var truncated_data = _.truncate(options.data, 255);
    var endpoint = options.endpoint;
    var batcher = options.batcher;
    var should_send_immediately = options.should_send_immediately;
    var send_request_options = options.send_request_options || {};
    callback = callback || NOOP_FUNC;

    var request_enqueued_or_initiated = true;
    var send_request_immediately = _.bind(function() {
        if (!send_request_options.skip_hooks) {
            truncated_data = this._run_hook('before_send_' + options.type, truncated_data);
        }
        if (truncated_data) {
            console.log('MIXPANEL REQUEST:');
            console.log(truncated_data);
            return this._send_request(
                endpoint,
                this._encode_data_for_request(truncated_data),
                send_request_options,
                this._prepare_callback(callback, truncated_data)
            );
        } else {
            return null;
        }
    }, this);

    if (this._batch_requests && !should_send_immediately) {
        batcher.enqueue(truncated_data).then(function(succeeded) {
            if (succeeded) {
                callback(1, truncated_data);
            } else {
                send_request_immediately();
            }
        });
    } else {
        request_enqueued_or_initiated = send_request_immediately();
    }

    return request_enqueued_or_initiated && truncated_data;
};