Browsers back button click with confirm box

Browsers back button click with confirm box

Need to create the javascript confirm pop up on click of browsers back
button. If I click on back button pop up will come up and say "you want to
go ahead ?" if click on Yes then it would have redirected to previous
page.
I have following code it is not working as per the requirement.
if(window.history && history.pushState){ // check for history api support
window.addEventListener('load', function(){
// create history states
history.pushState(-1, null); // back state
history.pushState(0, null); // main state
history.pushState(1, null); // forward state
history.go(-1); // start in main state
this.addEventListener('popstate', function(event, state){
// check history state and fire custom events
if(state = event.state){
event = document.createEvent('Event');
event.initEvent(state > 0 ? 'next' : 'previous', true,
true);
this.dispatchEvent(event);
var r = confirm("Would you like to save this draft?");
if(r==true) {
// Do nothing
} else {
self.location = document.referrer;
}
// reset state
history.go(-state);
}
}, false);
}, false);
}
Any help in this would be really appreciable.