Ionic 2 backbutton Event Listener

I want to achieve the click Back button, pop-up Toast box,Not quit
document.addEventListener(“backbutton”, () => {“I’m a toast”, “5000”, “center”).subscribe(
toast => {
// console.log(‘close’);

But actually,Quit App first, and then pop box Toast

this is works in ionic 2??
and r u have any code for device back button pressed event?
if u have please share with me.