Prevent to close browser or change page and show message javascript

Add this script before ending body tag.

<script>
window.onbeforeunload = function (evt) {
 var message = 'Do you want to leave this page?';
if (typeof evt == 'undefined') {
 evt = window.event;

}
 if (evt ) {
   evt.returnValue = message;
 }

    return message;

}
 onClick="return confirm('Do you want to leave this page?');"

</script>