Boomerang plugin that waits for the specified JavaScript variable to exist on the page before a beacon is sent.

boomerang-waitforjsvar-plugin.js

/**
 * The `WaitForJsVar` Boomerang plugin waits for the specified JavaScript variable
 * to exist on the page before a beacon is sent.
 *
 * It does not affect the Page Load time (`t_done`) -- it just delays a beacon
 * until the variable exists.  This allows the beacon to contain additional
 * ResourceTiming data and other metrics/timers that might happen after page load.
 *
 * NOTE: Any plugin like this that delays a beacon from being sent after onload
 * will have an effect on total number of beacons captured (due to the visitor
 * having more time to hard-close the browser, etc, before the beacon is sent).
 */
(function(w) {
    //
    // TODO: Configure the JavaScript variable you want to monitor below
    //
    var POLL_FREQUENCY = 100;

    if (!w) {
        return;
    }

    BOOMR = w.BOOMR || {};
    BOOMR.plugins = BOOMR.plugins || {};

    BOOMR.plugins.WaitForJsVar = {
        varFound: false, 

        init: function() {
            function poll() {
                //
                // TODO: Var check goes here
                //
                if (typeof w.TODO_JS_VARIABLE_TO_CHECK === "undefined") {
                    return setTimeout(poll, POLL_FREQUENCY);
                }

                this.varFound = true;

                if (typeof BOOMR.sendBeacon !== "function") {
                    return setTimeout(poll, POLL_FREQUENCY);
                }

                BOOMR.sendBeacon();
            }

            poll();
        },

        is_complete: function() {
            return this.varFound;
        }
    };
})(window);