Function for executing logic when closing the page/tab or navigating away

unload.js

var addUnloadEvent = function(unloadEvent, device) {

    // device is a object containing parsed user-agent information

    var executed = false,
      exec = function() {
        if (!executed) {
          executed = true;
          unloadEvent();
        }
      };
      
    if (device.type && device.type === "mobile") {
      document.addEventListener('visibilitychange', function() {
        if (document.visibilityState == 'hidden') {
            exec();
        }
      });
    }
    window.addEventListener("pagehide", exec);
    window.addEventListener("beforeunload", exec);
    window.onbeforeunload = exec;
    window.addEventListener('unload', exec);
}