The WaitAfterOnload Boomerang plugin waits for the specified number of seconds after * onload before a beacon is sent.

boomerang-wait-after-onload-plugin.js

/**
 * The `WaitAfterOnload` Boomerang plugin waits for the specified number of seconds after
 * onload before a beacon is sent.
 *
 * It does not affect the Page Load time (`t_done`) -- it just delays a beacon
 * for the specified number of seconds.  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 number of milliseconds you want to wait
    //
    var WAIT_AFTER_ONLOAD_MILLISECONDS = 3000;

    if (!w) {
        return;
    }

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

    BOOMR.plugins.WaitAfterOnload = {
        complete: false,

        init: function() {
            BOOMR.subscribe("page_ready", function() {
                setTimeout(function() {
                    this.complete = true;
                    BOOMR.sendBeacon();
                }.bind(this), WAIT_AFTER_ONLOAD_MILLISECONDS);
            }, {}, this);
        },

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