self.isAscending = true;
self.sortTitle = function () {
if(self.isAscending){
self.arr= self.arr.sort((a, b) => (a.title > b.title) ? 1 : -1);
}else{
self.arr= self.arr.sort((a, b) => (a.title > b.title) ? -1 : 1);
}
self.isAscending = !self.isAscending;
}