Boomerang plugin to repeat all beacons to a second URL.

boomerang-beaconrepeater.js

/**
 * Repeats all beacons to a second URL.
 *
 * To configure, update BEACON_URL.
 *
 * This code repeats some code from Boomerang.  If you only need to send
 * XHR beacons, or only image beacons, or not sendBeacon(), it could be trimmed down.
 *
 * @class BOOMR.plugins.BeaconRepeater
 */
(function() {
    BOOMR = window.BOOMR || {};
    BOOMR.plugins = BOOMR.plugins || {};

    if (BOOMR.plugins.BeaconRepeater) {
        return;
    }

    var BEACON_URL = "https://mybeaconurl.com/"

    //
    // Private implementation
    //
    var impl = {
        initialized: false,

        /**
         * Gets a URI-encoded name/value pair.
         *
         * @param {string} name Name
         * @param {string} value Value
         *
         * @returns {string} URI-encoded string
         *
         * @memberof BOOMR
         */
        getUriEncodedVar: function(name, value) {
            if (value === undefined || value === null) {
                value = "";
            }

            if (typeof value === "object") {
                value = BOOMR.utils.serializeForUrl(value);
            }

            var result = encodeURIComponent(name) +
                "=" + encodeURIComponent(value);

            return result;
        },

        /**
         * Fired after the main Boomerang beacon is sent
         *
         * @param {object} data Beacon Data
         */
        onBeacon: function(data) {
            // send the beacon elsewhere after a short delay
            setTimeout(function() {
                var name, paramsJoined, url = [], useImg = false, w = BOOMR.window || window;

                for (name in data) {
                    // if this var is set, add it to our URL array
                    if (data.hasOwnProperty(name)) {
                        url.push(impl.getUriEncodedVar(name, typeof data[name] === "undefined" ? "" : data[name]));
                    }
                }

                paramsJoined = url.join("&");

                //
                // Try the sendBeacon API first.
                // But if beacon_type is set to "GET", dont attempt
                // sendBeacon API call
                //
                if (w && w.navigator &&
                    typeof w.navigator.sendBeacon === "function" &&
                    BOOMR.utils.isNative(w.navigator.sendBeacon) &&
                    typeof w.Blob === "function") {
                    // note we're using sendBeacon with &sb=1
                    var blobData = new w.Blob([paramsJoined + "&sb=1"], {
                        type: "application/x-www-form-urlencoded"
                    });

                    if (w.navigator.sendBeacon(BEACON_URL, blobData)) {
                        return true;
                    }

                    // sendBeacon was not successful, try Image or XHR beacons
                }

                // If we don't have XHR available, force an image beacon and hope
                // for the best
                if (!BOOMR.orig_XMLHttpRequest && (!w || !w.XMLHttpRequest)) {
                    useImg = true;
                }

                if (useImg) {
                    //
                    // Image beacon
                    //

                    // just in case Image isn't a valid constructor
                    try {
                        img = new Image();
                    }
                    catch (e) {
                        BOOMR.debug("Image is not a constructor, not sending a beacon");
                        return false;
                    }

                    img.src = url;
                }
                else {
                    //
                    // XHR beacon
                    //

                    // Send a form-encoded XHR POST beacon
                    xhr = new (w.orig_XMLHttpRequest || BOOMR.orig_XMLHttpRequest || w.XMLHttpRequest)();
                    try {
                        impl.sendXhrPostBeacon(xhr, paramsJoined);
                    }
                    catch (e) {
                        // if we had an exception with the window XHR object, try our IFRAME XHR
                        xhr = new BOOMR.boomerang_frame.XMLHttpRequest();
                        impl.sendXhrPostBeacon(xhr, paramsJoined);
                    }
                }
            }, 0);
        },

        /**
         * Sends XHR POST beacon data
         *
         * @param {object} data Beacon Data
         */
        sendXhrPostBeacon: function(xhr, paramsJoined) {
            xhr.open("POST", BEACON_URL);

            xhr.setRequestHeader("Content-type", "application/x-www-form-urlencoded");

            xhr.send(paramsJoined);
        },
    };

    //
    // Exports
    //
    BOOMR.plugins.BeaconRepeater = {
        /**
         * Initializes the plugin.
         *
         * This plugin does not have any configuration.
         *
         * @returns {@link BOOMR.plugins.BeaconRepeater} The BeaconRepeater plugin for chaining
         * @memberof BOOMR.plugins.BeaconRepeater
         */
        init: function() {
            if (!impl.initialized) {
                BOOMR.subscribe("beacon", impl.onBeacon, null, impl);

                impl.initialized = true;
            }

            return this;
        },

        /**
         * Whether or not this plugin is complete
         *
         * @returns {boolean} `true` if the plugin is complete
         * @memberof BOOMR.plugins.BeaconRepeater
         */
        is_complete: function() {
            return true;
        }
    };
}());

Minified (1,420 bytes):

!function(){if(BOOMR=window.BOOMR||{},BOOMR.plugins=BOOMR.plugins||{},!BOOMR.plugins.BeaconRepeater){var c="https://mybeaconurl.com/",s={initialized:!1,getUriEncodedVar:function(e,n){return null==n&&(n=""),"object"==typeof n&&(n=BOOMR.utils.serializeForUrl(n)),encodeURIComponent(e)+"="+encodeURIComponent(n)},onBeacon:function(a){setTimeout(function(){var e,n,t=[],o=!1,i=BOOMR.window||window;for(e in a)a.hasOwnProperty(e)&&t.push(s.getUriEncodedVar(e,void 0===a[e]?"":a[e]));if(n=t.join("&"),i&&i.navigator&&"function"==typeof i.navigator.sendBeacon&&BOOMR.utils.isNative(i.navigator.sendBeacon)&&"function"==typeof i.Blob){var r=new i.Blob([n+"&sb=1"],{type:"application/x-www-form-urlencoded"});if(i.navigator.sendBeacon(c,r))return!0}if(BOOMR.orig_XMLHttpRequest||i&&i.XMLHttpRequest||(o=!0),o){try{img=new Image}catch(e){return BOOMR.debug("Image is not a constructor, not sending a beacon"),!1}img.src=t}else{xhr=new(i.orig_XMLHttpRequest||BOOMR.orig_XMLHttpRequest||i.XMLHttpRequest);try{s.sendXhrPostBeacon(xhr,n)}catch(e){xhr=new BOOMR.boomerang_frame.XMLHttpRequest,s.sendXhrPostBeacon(xhr,n)}}},0)},sendXhrPostBeacon:function(e,n){e.open("POST",c),e.setRequestHeader("Content-type","application/x-www-form-urlencoded"),e.send(n)}};BOOMR.plugins.BeaconRepeater={init:function(){return s.initialized||(BOOMR.subscribe("beacon",s.onBeacon,null,s),s.initialized=!0),this},is_complete:function(){return!0}}}}();