Call function when alert message is fired

I want to know which Dom event is fired when alert message is called. I want to call start_tracking method when alert message is called. I am able to call methods on page resize but how can i know which method is called when the alert message is fired.

win.addEventListener("click", function(event) {
      start_tracking ();
});

Click event is working when i am clicking anywhere on the page but when i click the alert message content then it does not fire the click listener. Nothing seems to be fired on the alert() function.