Remove data from Firebase with Ionic 3

I want to remove a data from firebase but all documents I have found all said use .remove() function as I show as codesnippet here. But this is not work at Ionic 3. Is that function is changed or what is the point that I didn't see.

selectBook(indexOfBook : Book){

this.actionSheetCtrl.create({
title: indexOfBook.nameOfBook,
buttons:[{
text:'Edit',
handler: () =>{
// TODO:Send the user to EditPage
}

},
{
text:'Delete',
role: 'destructive',
handler: () => {
this.getBookRef$.remove(indexOfBook.key);//**************************************
}
},
{
text:'Cancel',
role:'cancel',
handler: () =>{
console.log("The user has selected the cancel button");
}
}


]


}).present();

}

Continue reading...