I am trying to create a custom pop up card when a person try to refresh the browser. I know how to show the pop up alert in the top of the browser using this.

window.onbeforeunload = function() {
    return 'Your upload will be lost if you leave the page, are you sure?';
};

But I want to create a pop up like this when user refresh the page. Can anyone explain me how I can do that.