Preserving onfocus

I'm currently using Sweetalert with Phaser, game engine.

Phaser works only when it gets focus of window. So there is a problem since Sweetalert change window.onfocus and doesn't restore that.

I guess the solution is simple :

1. store its previous window.onfocus in constructor
2. restore window.onfocus to previous version in 'sweetAlert.close' function