How to work with change detection?

Question

Angular

I can’t understand, here I have an array in the object

private obj = {
arr: []
}

This object is in the service, when I add data to it In the component that is connected to this service , change detection immediately fires and my data is drawn. But if suddenly, I do a cleanup of this array Then when I write to this array again, the detection of changes on this array does not work, and new data is not drawn. Similarly, if I have an array with objects
obj.arr.push(1)

obj.arr = []

arr = [
  {id:1,name:'Вася'},
  {id:2,name:'Петя'},
  ...
 ]

When deleting an object in this array with the key ( 1 ) , change detection stops working and when other objects are added, they are no longer tracked...