(function startPresenceHeartbeat() {
  const ping = function () {
    fetch("/api/presence/ping", {
      method: "POST",
      credentials: "same-origin",
      keepalive: true,
      headers: {
        "Content-Type": "application/json",
      },
      body: "{}",
    }).catch(function () {
      // ignore network issues; next interval will retry
    });
  };

  ping();
  setInterval(ping, 15000);
})();