Confirm box before closing a tab

Question

I want to have a confirm box when user tries to close the window.

window.onbeforeunload = function (evt) {
    var mes         


        

Answer 1

I assume that on page load, you are setting up var sncro=1; and when some data changes, you adjust this value. Here is the quick check:

window.onbeforeunload = function (evt) {
  if (sncro != 1) {
   var message = 'Are you sure you want to leave, cause there are some unsaved changes?';
   if (typeof evt == 'undefined') {
      evt = window.event;
   }
   if (evt ) {
      evt.returnValue = message;
   }
   return message;
  }
}