Boomerang plugin that waits for the specified UserTiming Mark (or Measure) to exist on the page before a beacon is sent.

boomerang-waitformark-plugin.js

/**
 * The `WaitForMark` Boomerang plugin waits for the specified UserTiming Mark
 * (or Measure) 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 Mark 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 mark you want to wait for:
    //
    var MARK_NAME = "";

    var POLL_FREQUENCY = 100;

    if (!w || !("performance" in w) || !w.performance || typeof w.performance.getEntriesByName !== "function") {
        return;
    }

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

    BOOMR.plugins.WaitForMark = {
        markFound: false, 

        init: function() {
            function poll() {
                var entries = w.performance.getEntriesByName(MARK_NAME);
                if (entries.length == 0) {
                    return setTimeout(poll, POLL_FREQUENCY);
                }

                this.markFound = true;

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

                BOOMR.sendBeacon();
            }

            poll();
        },

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