JavaScript: Page change warning - alerts the user before allowing the window to close

page_change_warning.js

var PageChangeWarning = {
	unload_message: "You have unsaved changes on this page.",
	display_warning: function() {
		return this.unload_message;
	},
	change_made: function() {
		window.onbeforeunload = this.display_warning.bind(this);
	},
	saved: function() {
		window.onbeforeunload = null;
	}
};